diff --git a/transact/build.gradle.kts b/transact/build.gradle.kts
index 34032a30..a33e6202 100644
--- a/transact/build.gradle.kts
+++ b/transact/build.gradle.kts
@@ -31,6 +31,8 @@ dependencies {
     implementation("com.fasterxml.jackson.datatype:jackson-datatype-jsr310:2.17.0")
     implementation("com.cronutils:cron-utils:9.2.1") // cron for scheduled wf
 
+    compileOnly("org.jspecify:jspecify:1.0.0")
+
     testImplementation(platform("org.junit:junit-bom:5.12.1"))
     testImplementation("org.junit.jupiter:junit-jupiter")
     testImplementation("org.junit-pioneer:junit-pioneer:2.3.0")
diff --git a/transact/src/main/java/dev/dbos/transact/DBOS.java b/transact/src/main/java/dev/dbos/transact/DBOS.java
index 1865d0a5..eb68560d 100644
--- a/transact/src/main/java/dev/dbos/transact/DBOS.java
+++ b/transact/src/main/java/dev/dbos/transact/DBOS.java
@@ -32,6 +32,8 @@
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.atomic.AtomicReference;
 
+import org.jspecify.annotations.NonNull;
+import org.jspecify.annotations.Nullable;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -46,7 +48,7 @@ private DBOS() {}
   private static final Logger logger = LoggerFactory.getLogger(DBOS.class);
   private static final String version = loadVersionFromResources();
 
-  private static String loadVersionFromResources() {
+  private static @Nullable String loadVersionFromResources() {
     final String PROPERTIES_FILE = "/dev/dbos/transact/app.properties";
     final String VERSION_KEY = "app.version";
     Properties props = new Properties();
@@ -69,7 +71,7 @@ private static String loadVersionFromResources() {
     }
   }
 
-  public static String version() {
+  public static @Nullable String version() {
     return version;
   }
 
@@ -89,7 +91,9 @@ private Instance() {
     }
 
     private void registerClassWorkflows(
-        Class<?> interfaceClass, Object implementation, String instanceName) {
+        @NonNull Class<?> interfaceClass,
+        @NonNull Object implementation,
+        @Nullable String instanceName) {
       Objects.requireNonNull(interfaceClass, "interfaceClass must not be null");
       Objects.requireNonNull(implementation, "implementation must not be null");
       instanceName = Objects.requireNonNullElse(instanceName, "");
@@ -113,8 +117,12 @@ private void registerClassWorkflows(
       }
     }
 
-    private String registerWorkflowMethod(
-        Workflow wfTag, Object target, String className, String instanceName, Method method) {
+    private @NonNull String registerWorkflowMethod(
+        @NonNull Workflow wfTag,
+        @NonNull Object target,
+        @NonNull String className,
+        @NonNull String instanceName,
+        @NonNull Method method) {
       if (dbosExecutor.get() != null) {
         throw new IllegalStateException("Cannot register workflow after DBOS is launched");
       }
@@ -125,7 +133,7 @@ private String registerWorkflowMethod(
       return name;
     }
 
-    void registerLifecycleListener(DBOSLifecycleListener l) {
+    void registerLifecycleListener(@NonNull DBOSLifecycleListener l) {
       if (dbosExecutor.get() != null) {
         throw new IllegalStateException(
             "Cannot register lifecycle listener after DBOS is launched");
@@ -134,7 +142,7 @@ void registerLifecycleListener(DBOSLifecycleListener l) {
       lifecycleRegistry.add(l);
     }
 
-    void registerQueue(Queue queue) {
+    void registerQueue(@NonNull Queue queue) {
       if (dbosExecutor.get() != null) {
         throw new IllegalStateException("Cannot build a queue after DBOS is launched");
       }
@@ -142,11 +150,13 @@ void registerQueue(Queue queue) {
       queueRegistry.register(queue);
     }
 
-    public <T> T registerWorkflows(Class<T> interfaceClass, T implementation) {
+    public <T> @NonNull T registerWorkflows(
+        @NonNull Class<T> interfaceClass, @NonNull T implementation) {
       return registerWorkflows(interfaceClass, implementation, "");
     }
 
-    public <T> T registerWorkflows(Class<T> interfaceClass, T implementation, String instanceName) {
+    public <T> @NonNull T registerWorkflows(
+        @NonNull Class<T> interfaceClass, @NonNull T implementation, @NonNull String instanceName) {
       registerClassWorkflows(interfaceClass, implementation, instanceName);
 
       return DBOSInvocationHandler.createProxy(
@@ -169,11 +179,11 @@ void clearRegistry() {
     }
 
     // package private methods for test purposes
-    DBOSExecutor getDbosExecutor() {
+    @Nullable DBOSExecutor getDbosExecutor() {
       return dbosExecutor.get();
     }
 
-    public void setConfig(DBOSConfig config) {
+    public void setConfig(@NonNull DBOSConfig config) {
       if (this.config != null) {
         throw new IllegalStateException("DBOS has already been configured");
       }
@@ -230,7 +240,8 @@ public void shutdown() {
    * @return A proxy, with interface {@literal <T>}, that provides durability for the workflow
    *     functions
    */
-  public static <T> T registerWorkflows(Class<T> interfaceClass, T implementation) {
+  public static <T> @NonNull T registerWorkflows(
+      @NonNull Class<T> interfaceClass, @NonNull T implementation) {
     return ensureInstance().registerWorkflows(interfaceClass, implementation, "");
   }
 
@@ -245,8 +256,8 @@ public static <T> T registerWorkflows(Class<T> interfaceClass, T implementation)
    * @return A proxy, with interface {@literal <T>}, that provides durability for the workflow
    *     functions
    */
-  public static <T> T registerWorkflows(
-      Class<T> interfaceClass, T implementation, String instanceName) {
+  public static <T> @NonNull T registerWorkflows(
+      @NonNull Class<T> interfaceClass, @NonNull T implementation, @NonNull String instanceName) {
     return ensureInstance().registerWorkflows(interfaceClass, implementation, instanceName);
   }
 
@@ -257,7 +268,7 @@ public static <T> T registerWorkflows(
    * @param queue `Queue` to register
    * @return input queue
    */
-  public static Queue registerQueue(Queue queue) {
+  public static @NonNull Queue registerQueue(@NonNull Queue queue) {
     ensureInstance().registerQueue(queue);
     return queue;
   }
@@ -267,7 +278,7 @@ public static Queue registerQueue(Queue queue) {
    *
    * @param listener
    */
-  public static void registerLifecycleListener(DBOSLifecycleListener listener) {
+  public static void registerLifecycleListener(@NonNull DBOSLifecycleListener listener) {
     ensureInstance().registerLifecycleListener(listener);
   }
 
@@ -316,9 +327,9 @@ public static void shutdown() {
     if (globalInstance != null) globalInstance.shutdown();
   }
 
-  private static Instance globalInstance = null;
+  private static @Nullable Instance globalInstance = null;
 
-  public static Instance instance() {
+  public static @Nullable Instance instance() {
     return globalInstance;
   }
 
@@ -346,7 +357,7 @@ static DBOSExecutor executor(String caller) {
    *
    * @return Current workflow ID
    */
-  public static String workflowId() {
+  public static @Nullable String workflowId() {
     return DBOSContext.workflowId();
   }
 
@@ -355,7 +366,7 @@ public static String workflowId() {
    *
    * @return Current step ID number
    */
-  public static Integer stepId() {
+  public static @Nullable Integer stepId() {
     return DBOSContext.stepId();
   }
 
@@ -379,7 +390,7 @@ public static boolean inStep() {
    * @param queueName Name of the queue
    * @return Queue definition for given `queueName`
    */
-  public static Optional<Queue> getQueue(String queueName) {
+  public static @NonNull Optional<Queue> getQueue(@NonNull String queueName) {
     return executor("getQueue").getQueue(queueName);
   }
 
@@ -389,7 +400,7 @@ public static Optional<Queue> getQueue(String queueName) {
    *
    * @param duration amount of time to sleep
    */
-  public static void sleep(Duration duration) {
+  public static void sleep(@NonNull Duration duration) {
     if (!inWorkflow()) {
       try {
         Thread.sleep(duration.toMillis());
@@ -416,8 +427,8 @@ public static void sleep(Duration duration) {
    * @param options Start workflow options
    * @return A handle to the enqueued or running workflow
    */
-  public static <T, E extends Exception> WorkflowHandle<T, E> startWorkflow(
-      ThrowingSupplier<T, E> supplier, StartWorkflowOptions options) {
+  public static <T, E extends Exception> @NonNull WorkflowHandle<T, E> startWorkflow(
+      @NonNull ThrowingSupplier<T, E> supplier, @NonNull StartWorkflowOptions options) {
     return executor("startWorkflow").startWorkflow(supplier, options);
   }
 
@@ -429,8 +440,8 @@ public static <T, E extends Exception> WorkflowHandle<T, E> startWorkflow(
    * @param supplier A lambda that calls exactly one workflow function
    * @return A handle to the enqueued or running workflow
    */
-  public static <T, E extends Exception> WorkflowHandle<T, E> startWorkflow(
-      ThrowingSupplier<T, E> supplier) {
+  public static <T, E extends Exception> @NonNull WorkflowHandle<T, E> startWorkflow(
+      @NonNull ThrowingSupplier<T, E> supplier) {
     return startWorkflow(supplier, new StartWorkflowOptions());
   }
 
@@ -442,8 +453,8 @@ public static <T, E extends Exception> WorkflowHandle<T, E> startWorkflow(
    * @param options Start workflow options
    * @return A handle to the enqueued or running workflow
    */
-  public static <E extends Exception> WorkflowHandle<Void, E> startWorkflow(
-      ThrowingRunnable<E> runnable, StartWorkflowOptions options) {
+  public static <E extends Exception> @NonNull WorkflowHandle<Void, E> startWorkflow(
+      @NonNull ThrowingRunnable<E> runnable, @NonNull StartWorkflowOptions options) {
     return startWorkflow(
         () -> {
           runnable.execute();
@@ -459,8 +470,8 @@ public static <E extends Exception> WorkflowHandle<Void, E> startWorkflow(
    * @param runnable A lambda that calls exactly one workflow function
    * @return A handle to the enqueued or running workflow
    */
-  public static <E extends Exception> WorkflowHandle<Void, E> startWorkflow(
-      ThrowingRunnable<E> runnable) {
+  public static <E extends Exception> @NonNull WorkflowHandle<Void, E> startWorkflow(
+      @NonNull ThrowingRunnable<E> runnable) {
     return startWorkflow(runnable, new StartWorkflowOptions());
   }
 
@@ -473,7 +484,7 @@ public static <E extends Exception> WorkflowHandle<Void, E> startWorkflow(
    * @return Return value of the workflow
    * @throws E if the workflow threw an exception
    */
-  public static <T, E extends Exception> T getResult(String workflowId) throws E {
+  public static <T, E extends Exception> T getResult(@NonNull String workflowId) throws E {
     return executor("getResult").<T, E>getResult(workflowId);
   }
 
@@ -483,7 +494,7 @@ public static <T, E extends Exception> T getResult(String workflowId) throws E {
    * @param workflowId ID of the workflow to query
    * @return Current workflow status for the provided workflowId, or null.
    */
-  public static WorkflowStatus getWorkflowStatus(String workflowId) {
+  public static @Nullable WorkflowStatus getWorkflowStatus(@NonNull String workflowId) {
     return executor("getWorkflowStatus").getWorkflowStatus(workflowId);
   }
 
@@ -496,7 +507,10 @@ public static WorkflowStatus getWorkflowStatus(String workflowId) {
    * @param idempotencyKey optional idempotency key for exactly-once send
    */
   public static void send(
-      String destinationId, Object message, String topic, String idempotencyKey) {
+      @NonNull String destinationId,
+      @NonNull Object message,
+      @NonNull String topic,
+      @Nullable String idempotencyKey) {
     executor("send")
         .send(destinationId, message, topic, instance().internalWorkflowsService, idempotencyKey);
   }
@@ -508,7 +522,8 @@ public static void send(
    * @param message message to be sent
    * @param topic topic to which the message is send
    */
-  public static void send(String destinationId, Object message, String topic) {
+  public static void send(
+      @NonNull String destinationId, @NonNull Object message, @NonNull String topic) {
     DBOS.send(destinationId, message, topic, null);
   }
 
@@ -519,7 +534,7 @@ public static void send(String destinationId, Object message, String topic) {
    * @param timeout duration after which the call times out
    * @return the message if there is one or else null
    */
-  public static Object recv(String topic, Duration timeout) {
+  public static @Nullable Object recv(@NonNull String topic, @NonNull Duration timeout) {
     return executor("recv").recv(topic, timeout);
   }
 
@@ -529,7 +544,7 @@ public static Object recv(String topic, Duration timeout) {
    * @param key identifier for published data
    * @param value data that is published
    */
-  public static void setEvent(String key, Object value) {
+  public static void setEvent(@NonNull String key, @NonNull Object value) {
     executor("setEvent").setEvent(key, value);
   }
 
@@ -541,7 +556,8 @@ public static void setEvent(String key, Object value) {
    * @param timeout time to wait for data before timing out
    * @return the published value or null
    */
-  public static Object getEvent(String workflowId, String key, Duration timeout) {
+  public static @Nullable Object getEvent(
+      @NonNull String workflowId, @NonNull String key, @NonNull Duration timeout) {
     logger.debug("Received getEvent for {} {}", workflowId, key);
 
     return executor("getEvent").getEvent(workflowId, key, timeout);
@@ -556,7 +572,7 @@ public static Object getEvent(String workflowId, String key, Duration timeout) {
    * @throws E
    */
   public static <T, E extends Exception> T runStep(
-      ThrowingSupplier<T, E> stepfunc, StepOptions opts) throws E {
+      @NonNull ThrowingSupplier<T, E> stepfunc, @NonNull StepOptions opts) throws E {
 
     return executor("runStep").runStepInternal(stepfunc, opts, null);
   }
@@ -569,8 +585,8 @@ public static <T, E extends Exception> T runStep(
    * @param name name of the step, for tracing and to record in the system database
    * @throws E
    */
-  public static <T, E extends Exception> T runStep(ThrowingSupplier<T, E> stepfunc, String name)
-      throws E {
+  public static <T, E extends Exception> T runStep(
+      @NonNull ThrowingSupplier<T, E> stepfunc, @NonNull String name) throws E {
 
     return executor("runStep").runStepInternal(stepfunc, new StepOptions(name), null);
   }
@@ -583,8 +599,8 @@ public static <T, E extends Exception> T runStep(ThrowingSupplier<T, E> stepfunc
    * @param opts step name, and retry options for running the step
    * @throws E
    */
-  public static <E extends Exception> void runStep(ThrowingRunnable<E> stepfunc, StepOptions opts)
-      throws E {
+  public static <E extends Exception> void runStep(
+      @NonNull ThrowingRunnable<E> stepfunc, @NonNull StepOptions opts) throws E {
     executor("runStep")
         .runStepInternal(
             () -> {
@@ -603,8 +619,8 @@ public static <E extends Exception> void runStep(ThrowingRunnable<E> stepfunc, S
    * @param name Name of the step, for tracing and recording in the system database
    * @throws E
    */
-  public static <E extends Exception> void runStep(ThrowingRunnable<E> stepfunc, String name)
-      throws E {
+  public static <E extends Exception> void runStep(
+      @NonNull ThrowingRunnable<E> stepfunc, @NonNull String name) throws E {
     runStep(stepfunc, new StepOptions(name));
   }
 
@@ -616,7 +632,8 @@ public static <E extends Exception> void runStep(ThrowingRunnable<E> stepfunc, S
    * @param workflowId id of the workflow
    * @return A handle to the workflow
    */
-  public static <T, E extends Exception> WorkflowHandle<T, E> resumeWorkflow(String workflowId) {
+  public static <T, E extends Exception> @NonNull WorkflowHandle<T, E> resumeWorkflow(
+      @NonNull String workflowId) {
     return executor("resumeWorkflow").resumeWorkflow(workflowId);
   }
 
@@ -627,7 +644,7 @@ public static <T, E extends Exception> WorkflowHandle<T, E> resumeWorkflow(Strin
    *
    * @param workflowId ID of the workflow to cancel
    */
-  public static void cancelWorkflow(String workflowId) {
+  public static void cancelWorkflow(@NonNull String workflowId) {
     executor("cancelWorkflow").cancelWorkflow(workflowId);
   }
 
@@ -642,8 +659,8 @@ public static void cancelWorkflow(String workflowId) {
    * @param options {@link ForkOptions} containing forkedWorkflowId, applicationVersion, timeout
    * @return handle to the workflow
    */
-  public static <T, E extends Exception> WorkflowHandle<T, E> forkWorkflow(
-      String workflowId, int startStep, ForkOptions options) {
+  public static <T, E extends Exception> @NonNull WorkflowHandle<T, E> forkWorkflow(
+      @NonNull String workflowId, int startStep, @NonNull ForkOptions options) {
     return executor("forkWorkflow").forkWorkflow(workflowId, startStep, options);
   }
 
@@ -657,8 +674,8 @@ public static <T, E extends Exception> WorkflowHandle<T, E> forkWorkflow(
    * @param startStep Start execution from this step. Prior steps copied over
    * @return handle to the workflow
    */
-  public static <T, E extends Exception> WorkflowHandle<T, E> forkWorkflow(
-      String workflowId, int startStep) {
+  public static <T, E extends Exception> @NonNull WorkflowHandle<T, E> forkWorkflow(
+      @NonNull String workflowId, int startStep) {
     return forkWorkflow(workflowId, startStep, new ForkOptions());
   }
 
@@ -671,7 +688,8 @@ public static <T, E extends Exception> WorkflowHandle<T, E> forkWorkflow(
    * @param workflowId ID of the workflow to retrieve
    * @return Workflow handle for the provided workflow ID
    */
-  public static <T, E extends Exception> WorkflowHandle<T, E> retrieveWorkflow(String workflowId) {
+  public static <T, E extends Exception> @NonNull WorkflowHandle<T, E> retrieveWorkflow(
+      @NonNull String workflowId) {
     return executor("retrieveWorkflow").retrieveWorkflow(workflowId);
   }
 
@@ -681,7 +699,7 @@ public static <T, E extends Exception> WorkflowHandle<T, E> retrieveWorkflow(Str
    * @param input {@link ListWorkflowsInput} parameters to query workflows
    * @return a list of workflow status {@link WorkflowStatus}
    */
-  public static List<WorkflowStatus> listWorkflows(ListWorkflowsInput input) {
+  public static @NonNull List<WorkflowStatus> listWorkflows(@NonNull ListWorkflowsInput input) {
     return executor("listWorkflows").listWorkflows(input);
   }
 
@@ -691,7 +709,7 @@ public static List<WorkflowStatus> listWorkflows(ListWorkflowsInput input) {
    * @param workflowId Id of the workflow whose steps to return
    * @return list of step information {@link StepInfo}
    */
-  public static List<StepInfo> listWorkflowSteps(String workflowId) {
+  public static @NonNull List<StepInfo> listWorkflowSteps(@NonNull String workflowId) {
     return executor("listWorkflowSteps").listWorkflowSteps(workflowId);
   }
 
@@ -700,7 +718,7 @@ public static List<StepInfo> listWorkflowSteps(String workflowId) {
    *
    * @return list of all registered workflow methods
    */
-  public static Collection<RegisteredWorkflow> getRegisteredWorkflows() {
+  public static @NonNull Collection<RegisteredWorkflow> getRegisteredWorkflows() {
     return executor("getRegisteredWorkflows").getWorkflows();
   }
 
@@ -709,7 +727,7 @@ public static Collection<RegisteredWorkflow> getRegisteredWorkflows() {
    *
    * @return list of all class instances containing registered workflow methods
    */
-  public static Collection<RegisteredWorkflowInstance> getRegisteredWorkflowInstances() {
+  public static @NonNull Collection<RegisteredWorkflowInstance> getRegisteredWorkflowInstances() {
     return executor("getRegisteredWorkflowInstances").getInstances();
   }
 
@@ -767,7 +785,7 @@ public static ExternalState upsertExternalState(ExternalState state) {
    * @throws RuntimeException if patching is not enabled in DBOS config or if called outside a
    *     workflow
    */
-  public static boolean patch(String patchName) {
+  public static boolean patch(@NonNull String patchName) {
     return executor("patch").patch(patchName);
   }
 
@@ -783,7 +801,7 @@ public static boolean patch(String patchName) {
    * @throws RuntimeException if patching is not enabled in DBOS config or if called outside a
    *     workflow
    */
-  public static boolean deprecatePatch(String patchName) {
+  public static boolean deprecatePatch(@NonNull String patchName) {
     return executor("deprecatePatch").deprecatePatch(patchName);
   }
 }
diff --git a/transact/src/main/java/dev/dbos/transact/DBOSClient.java b/transact/src/main/java/dev/dbos/transact/DBOSClient.java
index 02aeb476..4089b736 100644
--- a/transact/src/main/java/dev/dbos/transact/DBOSClient.java
+++ b/transact/src/main/java/dev/dbos/transact/DBOSClient.java
@@ -19,6 +19,8 @@
 import java.util.UUID;
 
 import com.zaxxer.hikari.HikariDataSource;
+import org.jspecify.annotations.NonNull;
+import org.jspecify.annotations.Nullable;
 
 /**
  * DBOSClient allows external programs to interact with DBOS apps via direct system database access.
@@ -27,14 +29,14 @@
  */
 public class DBOSClient implements AutoCloseable {
   private class WorkflowHandleClient<T, E extends Exception> implements WorkflowHandle<T, E> {
-    private String workflowId;
+    private @NonNull String workflowId;
 
-    public WorkflowHandleClient(String workflowId) {
+    public WorkflowHandleClient(@NonNull String workflowId) {
       this.workflowId = workflowId;
     }
 
     @Override
-    public String workflowId() {
+    public @NonNull String workflowId() {
       return workflowId;
     }
 
@@ -44,12 +46,12 @@ public T getResult() throws E {
     }
 
     @Override
-    public WorkflowStatus getStatus() {
+    public @Nullable WorkflowStatus getStatus() {
       return systemDatabase.getWorkflowStatus(workflowId);
     }
   }
 
-  private final SystemDatabase systemDatabase;
+  private final @NonNull SystemDatabase systemDatabase;
 
   /**
    * Construct a DBOSClient, by providing system database access credentials
@@ -58,7 +60,7 @@ public WorkflowStatus getStatus() {
    * @param user System database user
    * @param password System database credential / password
    */
-  public DBOSClient(String url, String user, String password) {
+  public DBOSClient(@NonNull String url, @NonNull String user, @NonNull String password) {
     this(url, user, password, null);
   }
 
@@ -70,7 +72,11 @@ public DBOSClient(String url, String user, String password) {
    * @param password System database credential / password
    * @param schema Database schema for DBOS tables
    */
-  public DBOSClient(String url, String user, String password, String schema) {
+  public DBOSClient(
+      @NonNull String url,
+      @NonNull String user,
+      @NonNull String password,
+      @Nullable String schema) {
     var dataSource = SystemDatabase.createDataSource(url, user, password, 0, 0);
     systemDatabase = new SystemDatabase(dataSource, schema);
   }
@@ -80,7 +86,7 @@ public DBOSClient(String url, String user, String password, String schema) {
    *
    * @param dataSource System database data source
    */
-  public DBOSClient(HikariDataSource dataSource) {
+  public DBOSClient(@NonNull HikariDataSource dataSource) {
     this(dataSource, null);
   }
 
@@ -90,7 +96,7 @@ public DBOSClient(HikariDataSource dataSource) {
    * @param dataSource System database data source
    * @param schema Database schema for DBOS tables
    */
-  public DBOSClient(HikariDataSource dataSource, String schema) {
+  public DBOSClient(@NonNull HikariDataSource dataSource, @Nullable String schema) {
     systemDatabase = new SystemDatabase(dataSource, schema);
   }
 
@@ -105,17 +111,17 @@ public void close() {
    * and app version, are optional, and should be set with `with` functions.
    */
   public record EnqueueOptions(
-      String workflowName,
-      String queueName,
-      String className,
-      String instanceName,
-      String workflowId,
-      String appVersion,
-      Duration timeout,
-      Instant deadline,
-      String deduplicationId,
-      Integer priority,
-      String queuePartitionKey) {
+      @NonNull String workflowName,
+      @NonNull String queueName,
+      @NonNull String className,
+      @NonNull String instanceName,
+      @Nullable String workflowId,
+      @Nullable String appVersion,
+      @Nullable Duration timeout,
+      @Nullable Instant deadline,
+      @Nullable String deduplicationId,
+      @Nullable Integer priority,
+      @Nullable String queuePartitionKey) {
 
     public EnqueueOptions {
       if (Objects.requireNonNull(workflowName, "EnqueueOptions workflowName must not be null")
@@ -159,7 +165,8 @@ public record EnqueueOptions(
     }
 
     /** Construct `EnqueueOptions` with a minimum set of required options */
-    public EnqueueOptions(String className, String workflowName, String queueName) {
+    public EnqueueOptions(
+        @NonNull String className, @NonNull String workflowName, @NonNull String queueName) {
       this(workflowName, queueName, className, "", null, null, null, null, null, null, null);
     }
 
@@ -169,7 +176,7 @@ public EnqueueOptions(String className, String workflowName, String queueName) {
      * @param className Class containing the workflow to enqueue
      * @return New `EnqueueOptions` with the class name set
      */
-    public EnqueueOptions withClassName(String className) {
+    public @NonNull EnqueueOptions withClassName(@NonNull String className) {
       return new EnqueueOptions(
           this.workflowName,
           this.queueName,
@@ -191,7 +198,7 @@ public EnqueueOptions withClassName(String className) {
      * @param workflowId Workflow idempotency ID to use
      * @return New `EnqueueOptions` with the workflow ID set
      */
-    public EnqueueOptions withWorkflowId(String workflowId) {
+    public @NonNull EnqueueOptions withWorkflowId(@Nullable String workflowId) {
       return new EnqueueOptions(
           this.workflowName,
           this.queueName,
@@ -213,7 +220,7 @@ public EnqueueOptions withWorkflowId(String workflowId) {
      * @param appVersion Application version to use for executing the workflow
      * @return New `EnqueueOptions` with the app version set
      */
-    public EnqueueOptions withAppVersion(String appVersion) {
+    public @NonNull EnqueueOptions withAppVersion(@Nullable String appVersion) {
       return new EnqueueOptions(
           this.workflowName,
           this.queueName,
@@ -235,7 +242,7 @@ public EnqueueOptions withAppVersion(String appVersion) {
      * @param timeout Duration of time, from start, before the workflow is canceled.
      * @return New `EnqueueOptions` with the timeout set
      */
-    public EnqueueOptions withTimeout(Duration timeout) {
+    public @NonNull EnqueueOptions withTimeout(@Nullable Duration timeout) {
       return new EnqueueOptions(
           this.workflowName,
           this.queueName,
@@ -257,7 +264,7 @@ public EnqueueOptions withTimeout(Duration timeout) {
      * @param deadline Instant after which the workflow will be canceled.
      * @return New `EnqueueOptions` with the deadline set
      */
-    public EnqueueOptions withDeadline(Instant deadline) {
+    public @NonNull EnqueueOptions withDeadline(@Nullable Instant deadline) {
       return new EnqueueOptions(
           this.workflowName,
           this.queueName,
@@ -279,7 +286,7 @@ public EnqueueOptions withDeadline(Instant deadline) {
      * @param deduplicationId Queue deduplication ID
      * @return New `EnqueueOptions` with the deduplication ID set
      */
-    public EnqueueOptions withDeduplicationId(String deduplicationId) {
+    public @NonNull EnqueueOptions withDeduplicationId(@Nullable String deduplicationId) {
       return new EnqueueOptions(
           this.workflowName,
           this.queueName,
@@ -301,7 +308,7 @@ public EnqueueOptions withDeduplicationId(String deduplicationId) {
      * @param instName Instance name registered within `DBOS.registerWorkflows`
      * @return New `EnqueueOptions` with the target instance name set
      */
-    public EnqueueOptions withInstanceName(String instName) {
+    public @NonNull EnqueueOptions withInstanceName(@Nullable String instName) {
       return new EnqueueOptions(
           this.workflowName,
           this.queueName,
@@ -322,7 +329,7 @@ public EnqueueOptions withInstanceName(String instName) {
      * @param priority Queue priority; if `null`, priority '0' will be used.
      * @return New `EnqueueOptions` with the priority set
      */
-    public EnqueueOptions withPriority(Integer priority) {
+    public @NonNull EnqueueOptions withPriority(@Nullable Integer priority) {
       return new EnqueueOptions(
           this.workflowName,
           this.queueName,
@@ -345,7 +352,7 @@ public EnqueueOptions withPriority(Integer priority) {
      * @param partitionKey the partition key to use for queue partitioning, can be null
      * @return a new EnqueueOptions instance with the specified partition key
      */
-    public EnqueueOptions withQueuePartitionKey(String partitionKey) {
+    public @NonNull EnqueueOptions withQueuePartitionKey(@Nullable String partitionKey) {
       return new EnqueueOptions(
           this.workflowName,
           this.queueName,
@@ -366,7 +373,7 @@ public EnqueueOptions withQueuePartitionKey(String partitionKey) {
      * @return The workflow idemptence ID
      */
     @Override
-    public String workflowId() {
+    public @Nullable String workflowId() {
       return workflowId != null && workflowId.isEmpty() ? null : workflowId;
     }
   }
@@ -380,8 +387,8 @@ public String workflowId() {
    * @param args Arguments to pass to the workflow function
    * @return WorkflowHandle for retrieving workflow ID, status, and results
    */
-  public <T, E extends Exception> WorkflowHandle<T, E> enqueueWorkflow(
-      EnqueueOptions options, Object[] args) {
+  public <T, E extends Exception> @NonNull WorkflowHandle<T, E> enqueueWorkflow(
+      @NonNull EnqueueOptions options, @Nullable Object[] args) {
 
     return DBOSExecutor.enqueueWorkflow(
         Objects.requireNonNull(
@@ -416,7 +423,11 @@ public <T, E extends Exception> WorkflowHandle<T, E> enqueueWorkflow(
    * @param topic Topic for the message
    * @param idempotencyKey If specified, use the value to ensure exactly-once send semantics
    */
-  public void send(String destinationId, Object message, String topic, String idempotencyKey) {
+  public void send(
+      @NonNull String destinationId,
+      @NonNull Object message,
+      @NonNull String topic,
+      @Nullable String idempotencyKey) {
     if (idempotencyKey == null) {
       idempotencyKey = UUID.randomUUID().toString();
     }
@@ -438,7 +449,8 @@ public void send(String destinationId, Object message, String topic, String idem
    * @param timeout Maximum time duration to wait before returning `null`
    * @return Workflow event value, or `null` if the timeout is hit.
    */
-  public Object getEvent(String targetId, String key, Duration timeout) {
+  public @Nullable Object getEvent(
+      @NonNull String targetId, @NonNull String key, @NonNull Duration timeout) {
     return systemDatabase.getEvent(targetId, key, timeout, null);
   }
 
@@ -451,7 +463,8 @@ public Object getEvent(String targetId, String key, Duration timeout) {
    * @param workflowId ID of the workflow to retrieve
    * @return A `WorkflowHandle` for the specified worflow ID
    */
-  public <T, E extends Exception> WorkflowHandle<T, E> retrieveWorkflow(String workflowId) {
+  public <T, E extends Exception> @NonNull WorkflowHandle<T, E> retrieveWorkflow(
+      @NonNull String workflowId) {
     return new WorkflowHandleClient<T, E>(workflowId);
   }
 
@@ -460,7 +473,7 @@ public <T, E extends Exception> WorkflowHandle<T, E> retrieveWorkflow(String wor
    *
    * @param workflowId ID of the workflow to cancel
    */
-  public void cancelWorkflow(String workflowId) {
+  public void cancelWorkflow(@NonNull String workflowId) {
     systemDatabase.cancelWorkflow(workflowId);
   }
 
@@ -472,7 +485,8 @@ public void cancelWorkflow(String workflowId) {
    * @param workflowId ID of the workflow to resume
    * @return `WorkflowHandle` for the resumed workflow
    */
-  public <T, E extends Exception> WorkflowHandle<T, E> resumeWorkflow(String workflowId) {
+  public <T, E extends Exception> @NonNull WorkflowHandle<T, E> resumeWorkflow(
+      @NonNull String workflowId) {
     systemDatabase.resumeWorkflow(workflowId);
     return retrieveWorkflow(workflowId);
   }
@@ -488,8 +502,8 @@ public <T, E extends Exception> WorkflowHandle<T, E> resumeWorkflow(String workf
    * @param options Options for forking;
    * @return `WorkflowHandle` for the new workflow
    */
-  public <T, E extends Exception> WorkflowHandle<T, E> forkWorkflow(
-      String originalWorkflowId, int startStep, ForkOptions options) {
+  public <T, E extends Exception> @NonNull WorkflowHandle<T, E> forkWorkflow(
+      @NonNull String originalWorkflowId, int startStep, @NonNull ForkOptions options) {
     var forkedWorkflowId = systemDatabase.forkWorkflow(originalWorkflowId, startStep, options);
     return retrieveWorkflow(forkedWorkflowId);
   }
@@ -500,7 +514,7 @@ public <T, E extends Exception> WorkflowHandle<T, E> forkWorkflow(
    * @param workflowId ID of the workflow to query for status
    * @return WorkflowStatus of the workflow, or empty if the workflow does not exist
    */
-  public Optional<WorkflowStatus> getWorkflowStatus(String workflowId) {
+  public @NonNull Optional<WorkflowStatus> getWorkflowStatus(@NonNull String workflowId) {
     return Optional.ofNullable(systemDatabase.getWorkflowStatus(workflowId));
   }
 
@@ -510,7 +524,7 @@ public Optional<WorkflowStatus> getWorkflowStatus(String workflowId) {
    * @param input Filter criteria to use for listing workflows
    * @return list of workflows matching the `ListWorkflowsInput` criteria
    */
-  public List<WorkflowStatus> listWorkflows(ListWorkflowsInput input) {
+  public @NonNull List<WorkflowStatus> listWorkflows(@NonNull ListWorkflowsInput input) {
     return systemDatabase.listWorkflows(input);
   }
 
@@ -520,7 +534,7 @@ public List<WorkflowStatus> listWorkflows(ListWorkflowsInput input) {
    * @param workflowId ID of the workflow to list
    * @return List of steps executed by the workflow
    */
-  public List<StepInfo> listWorkflowSteps(String workflowId) {
+  public @NonNull List<StepInfo> listWorkflowSteps(@NonNull String workflowId) {
     return systemDatabase.listWorkflowSteps(workflowId);
   }
 }
diff --git a/transact/src/main/java/dev/dbos/transact/StartWorkflowOptions.java b/transact/src/main/java/dev/dbos/transact/StartWorkflowOptions.java
index 949cedc4..13d574e2 100644
--- a/transact/src/main/java/dev/dbos/transact/StartWorkflowOptions.java
+++ b/transact/src/main/java/dev/dbos/transact/StartWorkflowOptions.java
@@ -7,6 +7,9 @@
 import java.time.Instant;
 import java.util.concurrent.TimeUnit;
 
+import org.jspecify.annotations.NonNull;
+import org.jspecify.annotations.Nullable;
+
 /**
  * Options for starting a workflow, including: Assigning the workflow idempotency ID Enqueuing, with
  * options Setting a timeout.
@@ -27,15 +30,17 @@
  *     distribute workflows across queue partitions for load balancing and ordered processing.
  */
 public record StartWorkflowOptions(
-    String workflowId,
-    Timeout timeout,
-    Instant deadline,
-    String queueName,
-    String deduplicationId,
-    Integer priority,
-    String queuePartitionKey) {
-
-  public StartWorkflowOptions {
+    @Nullable String workflowId,
+    @Nullable Timeout timeout,
+    @Nullable Instant deadline,
+    @Nullable String queueName,
+    @Nullable String deduplicationId,
+    @Nullable Integer priority,
+    @Nullable String queuePartitionKey) {
+
+  public
+  @NonNull
+  StartWorkflowOptions {
     if (timeout instanceof Timeout.Explicit explicit) {
       if (explicit.value().isNegative() || explicit.value().isZero()) {
         throw new IllegalArgumentException(
@@ -60,17 +65,21 @@ public record StartWorkflowOptions(
   }
 
   /** Construct with default options */
-  public StartWorkflowOptions() {
+  public
+  @NonNull
+  StartWorkflowOptions() {
     this(null, null, null, null, null, null, null);
   }
 
   /** Construct with a specified workflow ID */
-  public StartWorkflowOptions(String workflowId) {
+  public
+  @NonNull
+  StartWorkflowOptions(String workflowId) {
     this(workflowId, null, null, null, null, null, null);
   }
 
   /** Produces a new StartWorkflowOptions that overrides the ID assigned to the started workflow */
-  public StartWorkflowOptions withWorkflowId(String workflowId) {
+  public @NonNull StartWorkflowOptions withWorkflowId(@Nullable String workflowId) {
     return new StartWorkflowOptions(
         workflowId,
         this.timeout,
@@ -82,7 +91,7 @@ public StartWorkflowOptions withWorkflowId(String workflowId) {
   }
 
   /** Produces a new StartWorkflowOptions that overrides timeout value for the started workflow */
-  public StartWorkflowOptions withTimeout(Timeout timeout) {
+  public @NonNull StartWorkflowOptions withTimeout(@Nullable Timeout timeout) {
     return new StartWorkflowOptions(
         this.workflowId,
         timeout,
@@ -94,22 +103,22 @@ public StartWorkflowOptions withTimeout(Timeout timeout) {
   }
 
   /** Produces a new StartWorkflowOptions that overrides timeout value for the started workflow */
-  public StartWorkflowOptions withTimeout(Duration timeout) {
+  public @NonNull StartWorkflowOptions withTimeout(@NonNull Duration timeout) {
     return withTimeout(Timeout.of(timeout));
   }
 
   /** Produces a new StartWorkflowOptions that overrides timeout value for the started workflow */
-  public StartWorkflowOptions withTimeout(long value, TimeUnit unit) {
+  public @NonNull StartWorkflowOptions withTimeout(long value, @NonNull TimeUnit unit) {
     return withTimeout(Duration.ofNanos(unit.toNanos(value)));
   }
 
   /** Produces a new StartWorkflowOptions that removes the timeout behavior */
-  public StartWorkflowOptions withNoTimeout() {
+  public @NonNull StartWorkflowOptions withNoTimeout() {
     return withTimeout(Timeout.none());
   }
 
   /** Produces a new StartWorkflowOptions that overrides deadline value for the started workflow */
-  public StartWorkflowOptions withDeadline(Instant deadline) {
+  public @NonNull StartWorkflowOptions withDeadline(@Nullable Instant deadline) {
     return new StartWorkflowOptions(
         this.workflowId,
         this.timeout,
@@ -121,7 +130,7 @@ public StartWorkflowOptions withDeadline(Instant deadline) {
   }
 
   /** Produces a new StartWorkflowOptions that assigns the started workflow to a queue */
-  public StartWorkflowOptions withQueue(String queue) {
+  public @NonNull StartWorkflowOptions withQueue(@Nullable String queue) {
     return new StartWorkflowOptions(
         this.workflowId,
         this.timeout,
@@ -133,7 +142,7 @@ public StartWorkflowOptions withQueue(String queue) {
   }
 
   /** Produces a new StartWorkflowOptions that assigns the started workflow to a queue */
-  public StartWorkflowOptions withQueue(Queue queue) {
+  public @NonNull StartWorkflowOptions withQueue(@NonNull Queue queue) {
     return withQueue(queue.name());
   }
 
@@ -141,7 +150,7 @@ public StartWorkflowOptions withQueue(Queue queue) {
    * Produces a new StartWorkflowOptions that assigns a queue deduplication ID. Note that the queue
    * must also be specified.
    */
-  public StartWorkflowOptions withDeduplicationId(String deduplicationId) {
+  public @NonNull StartWorkflowOptions withDeduplicationId(@Nullable String deduplicationId) {
     return new StartWorkflowOptions(
         this.workflowId,
         this.timeout,
@@ -156,7 +165,7 @@ public StartWorkflowOptions withDeduplicationId(String deduplicationId) {
    * Produces a new StartWorkflowOptions that assigns a queue priority. Note that the queue must
    * also be specified and have prioritization enabled
    */
-  public StartWorkflowOptions withPriority(Integer priority) {
+  public @NonNull StartWorkflowOptions withPriority(@Nullable Integer priority) {
     return new StartWorkflowOptions(
         this.workflowId,
         this.timeout,
@@ -168,7 +177,7 @@ public StartWorkflowOptions withPriority(Integer priority) {
   }
 
   /** Produces a new StartWorkflowOptions that assigns a queue partition key */
-  public StartWorkflowOptions withQueuePartitionKey(String queuePartitionKey) {
+  public @NonNull StartWorkflowOptions withQueuePartitionKey(@Nullable String queuePartitionKey) {
     return new StartWorkflowOptions(
         this.workflowId,
         this.timeout,
@@ -181,7 +190,7 @@ public StartWorkflowOptions withQueuePartitionKey(String queuePartitionKey) {
 
   /** Get the assigned workflow ID, replacing empty with null */
   @Override
-  public String workflowId() {
+  public @Nullable String workflowId() {
     return workflowId != null && workflowId.isEmpty() ? null : workflowId;
   }
 }
diff --git a/transact/src/main/java/dev/dbos/transact/config/DBOSConfig.java b/transact/src/main/java/dev/dbos/transact/config/DBOSConfig.java
index 311fb428..201dbb61 100644
--- a/transact/src/main/java/dev/dbos/transact/config/DBOSConfig.java
+++ b/transact/src/main/java/dev/dbos/transact/config/DBOSConfig.java
@@ -3,23 +3,25 @@
 import dev.dbos.transact.Constants;
 
 import com.zaxxer.hikari.HikariDataSource;
+import org.jspecify.annotations.NonNull;
+import org.jspecify.annotations.Nullable;
 
 public record DBOSConfig(
-    String appName,
-    String databaseUrl,
-    String dbUser,
-    String dbPassword,
+    @NonNull String appName,
+    @Nullable String databaseUrl,
+    @Nullable String dbUser,
+    @Nullable String dbPassword,
     int maximumPoolSize,
     int connectionTimeout,
-    HikariDataSource dataSource,
+    @Nullable HikariDataSource dataSource,
     boolean adminServer,
     int adminServerPort,
     boolean migrate,
-    String conductorKey,
-    String conductorDomain,
-    String appVersion,
-    String executorId,
-    String databaseSchema,
+    @Nullable String conductorKey,
+    @Nullable String conductorDomain,
+    @Nullable String appVersion,
+    @Nullable String executorId,
+    @Nullable String databaseSchema,
     boolean enablePatching) {
 
   public DBOSConfig {
@@ -41,7 +43,7 @@ public record DBOSConfig(
     }
   }
 
-  public static DBOSConfig defaults(String appName) {
+  public static @NonNull DBOSConfig defaults(@NonNull String appName) {
     return new DBOSConfig(
         appName, null, null, null, 3, // maximumPoolSize default
         30000, // connectionTimeout default
@@ -51,7 +53,7 @@ public static DBOSConfig defaults(String appName) {
         null, null, null, null, null, false);
   }
 
-  public static DBOSConfig defaultsFromEnv(String appName) {
+  public static @NonNull DBOSConfig defaultsFromEnv(@NonNull String appName) {
     String databaseUrl = System.getenv(Constants.SYSTEM_JDBC_URL_ENV_VAR);
     String dbUser = System.getenv(Constants.POSTGRES_USER_ENV_VAR);
     if (dbUser == null || dbUser.isEmpty()) dbUser = "postgres";
@@ -62,7 +64,7 @@ public static DBOSConfig defaultsFromEnv(String appName) {
         .withDbPassword(dbPassword);
   }
 
-  public DBOSConfig withAppName(String v) {
+  public @NonNull DBOSConfig withAppName(@NonNull String v) {
     return new DBOSConfig(
         v,
         databaseUrl,
@@ -82,7 +84,7 @@ public DBOSConfig withAppName(String v) {
         enablePatching);
   }
 
-  public DBOSConfig withDatabaseUrl(String v) {
+  public @NonNull DBOSConfig withDatabaseUrl(@Nullable String v) {
     return new DBOSConfig(
         appName,
         v,
@@ -102,7 +104,7 @@ public DBOSConfig withDatabaseUrl(String v) {
         enablePatching);
   }
 
-  public DBOSConfig withDbUser(String v) {
+  public @NonNull DBOSConfig withDbUser(@Nullable String v) {
     return new DBOSConfig(
         appName,
         databaseUrl,
@@ -122,7 +124,7 @@ public DBOSConfig withDbUser(String v) {
         enablePatching);
   }
 
-  public DBOSConfig withDbPassword(String v) {
+  public @NonNull DBOSConfig withDbPassword(@Nullable String v) {
     return new DBOSConfig(
         appName,
         databaseUrl,
@@ -142,7 +144,7 @@ public DBOSConfig withDbPassword(String v) {
         enablePatching);
   }
 
-  public DBOSConfig withMaximumPoolSize(int v) {
+  public @NonNull DBOSConfig withMaximumPoolSize(int v) {
     return new DBOSConfig(
         appName,
         databaseUrl,
@@ -162,7 +164,7 @@ public DBOSConfig withMaximumPoolSize(int v) {
         enablePatching);
   }
 
-  public DBOSConfig withConnectionTimeout(int v) {
+  public @NonNull DBOSConfig withConnectionTimeout(int v) {
     return new DBOSConfig(
         appName,
         databaseUrl,
@@ -182,7 +184,7 @@ public DBOSConfig withConnectionTimeout(int v) {
         enablePatching);
   }
 
-  public DBOSConfig withDataSource(HikariDataSource v) {
+  public @NonNull DBOSConfig withDataSource(@Nullable HikariDataSource v) {
     return new DBOSConfig(
         appName,
         databaseUrl,
@@ -202,7 +204,7 @@ public DBOSConfig withDataSource(HikariDataSource v) {
         enablePatching);
   }
 
-  public DBOSConfig withAdminServer(boolean v) {
+  public @NonNull DBOSConfig withAdminServer(boolean v) {
     return new DBOSConfig(
         appName,
         databaseUrl,
@@ -222,7 +224,7 @@ public DBOSConfig withAdminServer(boolean v) {
         enablePatching);
   }
 
-  public DBOSConfig withAdminServerPort(int v) {
+  public @NonNull DBOSConfig withAdminServerPort(int v) {
     return new DBOSConfig(
         appName,
         databaseUrl,
@@ -242,7 +244,7 @@ public DBOSConfig withAdminServerPort(int v) {
         enablePatching);
   }
 
-  public DBOSConfig withMigrate(boolean v) {
+  public @NonNull DBOSConfig withMigrate(boolean v) {
     return new DBOSConfig(
         appName,
         databaseUrl,
@@ -262,7 +264,7 @@ public DBOSConfig withMigrate(boolean v) {
         enablePatching);
   }
 
-  public DBOSConfig withConductorKey(String v) {
+  public @NonNull DBOSConfig withConductorKey(@Nullable String v) {
     return new DBOSConfig(
         appName,
         databaseUrl,
@@ -282,7 +284,7 @@ public DBOSConfig withConductorKey(String v) {
         enablePatching);
   }
 
-  public DBOSConfig withConductorDomain(String v) {
+  public @NonNull DBOSConfig withConductorDomain(@Nullable String v) {
     return new DBOSConfig(
         appName,
         databaseUrl,
@@ -302,7 +304,7 @@ public DBOSConfig withConductorDomain(String v) {
         enablePatching);
   }
 
-  public DBOSConfig withAppVersion(String v) {
+  public @NonNull DBOSConfig withAppVersion(@Nullable String v) {
     return new DBOSConfig(
         appName,
         databaseUrl,
@@ -322,7 +324,7 @@ public DBOSConfig withAppVersion(String v) {
         enablePatching);
   }
 
-  public DBOSConfig withExecutorId(String v) {
+  public @NonNull DBOSConfig withExecutorId(@Nullable String v) {
     return new DBOSConfig(
         appName,
         databaseUrl,
@@ -342,7 +344,7 @@ public DBOSConfig withExecutorId(String v) {
         enablePatching);
   }
 
-  public DBOSConfig withDatabaseSchema(String v) {
+  public @NonNull DBOSConfig withDatabaseSchema(@Nullable String v) {
     return new DBOSConfig(
         appName,
         databaseUrl,
@@ -362,15 +364,15 @@ public DBOSConfig withDatabaseSchema(String v) {
         enablePatching);
   }
 
-  public DBOSConfig withEnablePatching() {
+  public @NonNull DBOSConfig withEnablePatching() {
     return this.withEnablePatching(true);
   }
 
-  public DBOSConfig withDisablePatching() {
+  public @NonNull DBOSConfig withDisablePatching() {
     return this.withEnablePatching(false);
   }
 
-  public DBOSConfig withEnablePatching(boolean v) {
+  public @NonNull DBOSConfig withEnablePatching(boolean v) {
     return new DBOSConfig(
         appName,
         databaseUrl,
@@ -390,11 +392,11 @@ public DBOSConfig withEnablePatching(boolean v) {
         v);
   }
 
-  public DBOSConfig enableAdminServer() {
+  public @NonNull DBOSConfig enableAdminServer() {
     return withAdminServer(true);
   }
 
-  public DBOSConfig disableAdminServer() {
+  public @NonNull DBOSConfig disableAdminServer() {
     return withAdminServer(false);
   }
 
diff --git a/transact/src/main/java/dev/dbos/transact/context/WorkflowOptions.java b/transact/src/main/java/dev/dbos/transact/context/WorkflowOptions.java
index 6983229e..2ec14bed 100644
--- a/transact/src/main/java/dev/dbos/transact/context/WorkflowOptions.java
+++ b/transact/src/main/java/dev/dbos/transact/context/WorkflowOptions.java
@@ -6,6 +6,9 @@
 import java.time.Instant;
 import java.util.concurrent.TimeUnit;
 
+import org.jspecify.annotations.NonNull;
+import org.jspecify.annotations.Nullable;
+
 /**
  * The WorkflowOptions class is used to specify options for DBOS workflow functions that are invoked
  * synchronously. For example, the following construct will run a workflow under id `wfId`, and
@@ -16,7 +19,8 @@
  * @param timeout The timeout to be assigned to the next workflow in the DBOS context
  * @param deadline The deadline to be assigned to the next workflow in the DBOS context
  */
-public record WorkflowOptions(String workflowId, Timeout timeout, Instant deadline) {
+public record WorkflowOptions(
+    @Nullable String workflowId, @Nullable Timeout timeout, @Nullable Instant deadline) {
 
   public WorkflowOptions {
     if (timeout instanceof Timeout.Explicit explicit) {
@@ -33,17 +37,21 @@ public record WorkflowOptions(String workflowId, Timeout timeout, Instant deadli
   }
 
   /** Create a WorkflowOptions with no ID and no timout */
-  public WorkflowOptions() {
+  public
+  @NonNull
+  WorkflowOptions() {
     this(null, null, null);
   }
 
   /** Create a WorkflowOptions with a specified workflow ID and no timout */
-  public WorkflowOptions(String workflowId) {
+  public
+  @NonNull
+  WorkflowOptions(@Nullable String workflowId) {
     this(workflowId, null, null);
   }
 
   /** Create a WorkflowOptions like this one, but with the workflowId set */
-  public WorkflowOptions withWorkflowId(String workflowId) {
+  public @NonNull WorkflowOptions withWorkflowId(@Nullable String workflowId) {
     return new WorkflowOptions(workflowId, this.timeout, this.deadline);
   }
 
@@ -52,7 +60,7 @@ public WorkflowOptions withWorkflowId(String workflowId) {
    *
    * @param timeout timeout to use, expressed as a `dev.dbos.transact.workflow.Timeout`
    */
-  public WorkflowOptions withTimeout(Timeout timeout) {
+  public @NonNull WorkflowOptions withTimeout(@Nullable Timeout timeout) {
     return new WorkflowOptions(this.workflowId, timeout, this.deadline);
   }
 
@@ -61,7 +69,7 @@ public WorkflowOptions withTimeout(Timeout timeout) {
    *
    * @param timeout timeout to use, expressed as a `java.util.Duration`
    */
-  public WorkflowOptions withTimeout(Duration timeout) {
+  public @NonNull WorkflowOptions withTimeout(@NonNull Duration timeout) {
     return new WorkflowOptions(this.workflowId, Timeout.of(timeout), this.deadline);
   }
 
@@ -71,7 +79,7 @@ public WorkflowOptions withTimeout(Duration timeout) {
    * @param value timeout value to use, expressed as a value (see `unit`)
    * @param unit units to use for interpreting timeout `value`
    */
-  public WorkflowOptions withTimeout(long value, TimeUnit unit) {
+  public @NonNull WorkflowOptions withTimeout(long value, @NonNull TimeUnit unit) {
     return withTimeout(Duration.ofNanos(unit.toNanos(value)));
   }
 
@@ -80,12 +88,12 @@ public WorkflowOptions withTimeout(long value, TimeUnit unit) {
    *
    * @param deadline deadline to use, expressed as a `java.util.Instant`
    */
-  public WorkflowOptions withDeadline(Instant deadline) {
+  public @NonNull WorkflowOptions withDeadline(@Nullable Instant deadline) {
     return new WorkflowOptions(this.workflowId, this.timeout, deadline);
   }
 
   /** Create a workflow options like this one, but without a timeout */
-  public WorkflowOptions withNoTimeout() {
+  public @NonNull WorkflowOptions withNoTimeout() {
     return new WorkflowOptions(this.workflowId, Timeout.none(), this.deadline);
   }
 
@@ -93,7 +101,7 @@ public WorkflowOptions withNoTimeout() {
    * @return The workflow ID that will be used
    */
   @Override
-  public String workflowId() {
+  public @Nullable String workflowId() {
     return workflowId != null && workflowId.isEmpty() ? null : workflowId;
   }
 
@@ -102,7 +110,7 @@ public String workflowId() {
    * Should be called as an AutoCloseable so that the context is restored at the end of the block.
    * try (var _i = new WorkflowOptions(...).setContext()) { ... }
    */
-  public Guard setContext() {
+  public @NonNull Guard setContext() {
     var ctx = DBOSContextHolder.get();
     var guard = new Guard(ctx);
 
@@ -126,7 +134,9 @@ public static class Guard implements AutoCloseable {
     private final Timeout timeout;
     private final Instant deadline;
 
-    private Guard(DBOSContext ctx) {
+    private
+    @NonNull
+    Guard(@NonNull DBOSContext ctx) {
       this.ctx = ctx;
       this.nextWorkflowId = ctx.nextWorkflowId;
       this.timeout = ctx.nextTimeout;