diff --git a/api-generation/src/main/scala/ai/h2o/sparkling/api/generation/common/MetricResolver.scala b/api-generation/src/main/scala/ai/h2o/sparkling/api/generation/common/MetricResolver.scala
index 8712dee3ba..bceba1415e 100644
--- a/api-generation/src/main/scala/ai/h2o/sparkling/api/generation/common/MetricResolver.scala
+++ b/api-generation/src/main/scala/ai/h2o/sparkling/api/generation/common/MetricResolver.scala
@@ -30,6 +30,6 @@ trait MetricResolver {
           val (swFieldName, swMetricName) = MetricNameConverter.convertFromH2OToSW(field.getName)
           Metric(swFieldName, swMetricName, field.getName, field.getType, field.getAnnotation(classOf[API]).help())
         }
-    parameters
+    parameters.toSeq
   }
 }
diff --git a/core/src/main/scala/ai/h2o/sparkling/H2OColumnType.scala b/core/src/main/scala/ai/h2o/sparkling/H2OColumnType.scala
index f2e6d3fb26..84de5b8e29 100644
--- a/core/src/main/scala/ai/h2o/sparkling/H2OColumnType.scala
+++ b/core/src/main/scala/ai/h2o/sparkling/H2OColumnType.scala
@@ -18,7 +18,7 @@
 package ai.h2o.sparkling
 
 object H2OColumnType extends Enumeration {
-  val enum, string, int, real, time, uuid = Value
+  val `enum`, string, int, real, time, uuid = Value
 
   def fromString(dataType: String): Value = {
     values.find(_.toString == dataType).getOrElse(throw new RuntimeException(s"Unknown H2O's Data type $dataType"))
diff --git a/core/src/main/scala/ai/h2o/sparkling/H2OContext.scala b/core/src/main/scala/ai/h2o/sparkling/H2OContext.scala
index fffca7456c..07eea029b3 100644
--- a/core/src/main/scala/ai/h2o/sparkling/H2OContext.scala
+++ b/core/src/main/scala/ai/h2o/sparkling/H2OContext.scala
@@ -123,7 +123,7 @@ class H2OContext private[sparkling] (private val conf: H2OConf) extends H2OConte
       cloudV3.compiled_on)
     val h2oClusterInfo = H2OClusterInfo(
       s"$flowIp:$flowPort",
-      visibleFlowURL,
+      visibleFlowURL(),
       cloudV3.cloud_healthy,
       cloudV3.internal_security_enabled,
       nodes.map(_.ipPort()),
@@ -305,7 +305,7 @@ class H2OContext private[sparkling] (private val conf: H2OConf) extends H2OConte
          |  ${nodes.mkString("\n  ")}
          |  ------------------------
          |
-         |  Open H2O Flow in browser: ${getFlowUIHint}
+         |  Open H2O Flow in browser: ${getFlowUIHint()}
          |
     """.stripMargin
     val sparkYarnAppId = if (sparkContext.master.toLowerCase.startsWith("yarn")) {
@@ -475,8 +475,8 @@ object H2OContext extends Logging {
 
   private def logStartingInfo(conf: H2OConf): Unit = {
     logInfo("Sparkling Water version: " + BuildInfo.SWVersion)
-    val unsupportedSuffix = if (getFirstUnsupportedSWVersion.isDefined) " (unsupported)" else ""
-    val deprecationSuffix = if (isSparkVersionDeprecated) " (deprecated)" else ""
+    val unsupportedSuffix = if (getFirstUnsupportedSWVersion().isDefined) " (unsupported)" else ""
+    val deprecationSuffix = if (isSparkVersionDeprecated()) " (deprecated)" else ""
     logInfo("Spark version: " + SparkSessionUtils.active.version + unsupportedSuffix + deprecationSuffix)
     logInfo("Integrated H2O version: " + BuildInfo.H2OVersion)
     logInfo("The following Spark configuration is used: \n    " + conf.getAll.mkString("\n    "))
@@ -502,7 +502,7 @@ object H2OContext extends Logging {
         s"Apache Spark ${SparkSessionUtils.active.version} is unsupported" +
           s"since the Sparkling Water version ${unsupportedSWVersion.get}.")
     }
-    if (isSparkVersionDeprecated) {
+    if (isSparkVersionDeprecated()) {
       logWarning(
         s"Apache Spark ${SparkSessionUtils.active.version} is deprecated and " +
           "the support will be removed in the Sparkling Water version 3.44.")
diff --git a/core/src/main/scala/ai/h2o/sparkling/H2OFrame.scala b/core/src/main/scala/ai/h2o/sparkling/H2OFrame.scala
index a9a016f7d0..7e770ef736 100644
--- a/core/src/main/scala/ai/h2o/sparkling/H2OFrame.scala
+++ b/core/src/main/scala/ai/h2o/sparkling/H2OFrame.scala
@@ -151,7 +151,7 @@ class H2OFrame private (
       this
     } else {
       val endpoint = getClusterEndpoint(conf)
-      val colIndices = columns.map(columnNames.indexOf)
+      val colIndices = columns.map(col => columnNames.indexOf(col))
       val newFrameId = s"${frameId}_subframe_${colIndices.mkString("_")}"
       val params = Map(
         "ast" -> MessageFormat.format(s"( assign {0} (cols {1} {2}))", newFrameId, frameId, stringifyArray(colIndices)))
diff --git a/core/src/main/scala/ai/h2o/sparkling/SparklingWaterDriver.scala b/core/src/main/scala/ai/h2o/sparkling/SparklingWaterDriver.scala
index 92bc69bee5..aa1461c39c 100644
--- a/core/src/main/scala/ai/h2o/sparkling/SparklingWaterDriver.scala
+++ b/core/src/main/scala/ai/h2o/sparkling/SparklingWaterDriver.scala
@@ -27,7 +27,7 @@ import org.apache.spark.SparkConf
 object SparklingWaterDriver {
 
   /** Entry point */
-  def main(args: Array[String]) {
+  def main(args: Array[String]): Unit = {
     // Configure this application
     val conf: SparkConf = H2OConf.checkSparkConf(
       new SparkConf()
diff --git a/core/src/main/scala/ai/h2o/sparkling/backend/H2ODataFrame.scala b/core/src/main/scala/ai/h2o/sparkling/backend/H2ODataFrame.scala
index 0e9d3cc56f..031614adf2 100644
--- a/core/src/main/scala/ai/h2o/sparkling/backend/H2ODataFrame.scala
+++ b/core/src/main/scala/ai/h2o/sparkling/backend/H2ODataFrame.scala
@@ -51,7 +51,7 @@ private[backend] class H2ODataFrame(val frame: H2OFrame, val requiredColumns: Ar
     if (requiredColumns == null) {
       colNames.indices.toArray
     } else {
-      requiredColumns.map(colNames.indexOf)
+      requiredColumns.map(col => colNames.indexOf(col))
     }
   }
 
diff --git a/core/src/main/scala/ai/h2o/sparkling/backend/H2ORDD.scala b/core/src/main/scala/ai/h2o/sparkling/backend/H2ORDD.scala
index ec7baeeb56..c3102869d2 100644
--- a/core/src/main/scala/ai/h2o/sparkling/backend/H2ORDD.scala
+++ b/core/src/main/scala/ai/h2o/sparkling/backend/H2ORDD.scala
@@ -92,7 +92,7 @@ private[backend] class H2ORDD[A <: Product: TypeTag: ClassTag](val frame: H2OFra
   private def columnReaders(rcc: Reader) = {
     val readerMapByName = (rcc.OptionReaders ++ rcc.SimpleReaders).map {
       case (supportedType, reader) => supportedType.name -> reader
-    }
+    }.toMap
     productType.memberTypeNames.map(name => readerMapByName(name))
   }
 
diff --git a/core/src/main/scala/ai/h2o/sparkling/backend/converters/SupportedDataset.scala b/core/src/main/scala/ai/h2o/sparkling/backend/converters/SupportedDataset.scala
index 480d6d1b37..9d62c6426f 100644
--- a/core/src/main/scala/ai/h2o/sparkling/backend/converters/SupportedDataset.scala
+++ b/core/src/main/scala/ai/h2o/sparkling/backend/converters/SupportedDataset.scala
@@ -162,7 +162,7 @@ private[this] object SupportedDataset {
       override def toH2OFrame(hc: H2OContext, frameKeyName: Option[String]): H2OFrame = {
         val spark = SparkSessionUtils.active
         import spark.implicits._
-        SparkDataFrameConverter.toH2OFrame(hc, dataset.map(v => Tuple1(v)).toDF, frameKeyName)
+        SparkDataFrameConverter.toH2OFrame(hc, dataset.map(v => Tuple1(v)).toDF(), frameKeyName)
       }
     }
 
@@ -171,7 +171,7 @@ private[this] object SupportedDataset {
       override def toH2OFrame(hc: H2OContext, frameKeyName: Option[String]): H2OFrame = {
         val spark = SparkSessionUtils.active
         import spark.implicits._
-        SparkDataFrameConverter.toH2OFrame(hc, dataset.map(v => Tuple1(v)).toDF, frameKeyName)
+        SparkDataFrameConverter.toH2OFrame(hc, dataset.map(v => Tuple1(v)).toDF(), frameKeyName)
       }
     }
 }
diff --git a/core/src/main/scala/ai/h2o/sparkling/backend/converters/SupportedRDD.scala b/core/src/main/scala/ai/h2o/sparkling/backend/converters/SupportedRDD.scala
index 5b7ed744d8..48793e1559 100644
--- a/core/src/main/scala/ai/h2o/sparkling/backend/converters/SupportedRDD.scala
+++ b/core/src/main/scala/ai/h2o/sparkling/backend/converters/SupportedRDD.scala
@@ -191,7 +191,7 @@ private[this] object SupportedRDD {
     override def toH2OFrame(hc: H2OContext, frameKeyName: Option[String]): H2OFrame = {
       val spark = SparkSessionUtils.active
       import spark.implicits._
-      SparkDataFrameConverter.toH2OFrame(hc, rdd.map(v => Tuple1(v)).toDF, frameKeyName)
+      SparkDataFrameConverter.toH2OFrame(hc, rdd.map(v => Tuple1(v)).toDF(), frameKeyName)
     }
   }
 
@@ -199,7 +199,7 @@ private[this] object SupportedRDD {
     override def toH2OFrame(hc: H2OContext, frameKeyName: Option[String]): H2OFrame = {
       val spark = SparkSessionUtils.active
       import spark.implicits._
-      SparkDataFrameConverter.toH2OFrame(hc, rdd.map(v => Tuple1(v)).toDF, frameKeyName)
+      SparkDataFrameConverter.toH2OFrame(hc, rdd.map(v => Tuple1(v)).toDF(), frameKeyName)
     }
   }
 }
diff --git a/core/src/main/scala/ai/h2o/sparkling/backend/external/ExternalBackendConf.scala b/core/src/main/scala/ai/h2o/sparkling/backend/external/ExternalBackendConf.scala
index 79fcf04471..4c2d2d60cf 100644
--- a/core/src/main/scala/ai/h2o/sparkling/backend/external/ExternalBackendConf.scala
+++ b/core/src/main/scala/ai/h2o/sparkling/backend/external/ExternalBackendConf.scala
@@ -188,7 +188,7 @@ trait ExternalBackendConf extends SharedBackendConf with Logging with ExternalBa
 
   def setExternalExtraJars(commaSeparatedPaths: String): H2OConf = set(PROP_EXTERNAL_EXTRA_JARS._1, commaSeparatedPaths)
 
-  def setExternalExtraJars(paths: java.util.ArrayList[String]): H2OConf = setExternalExtraJars(paths.asScala)
+  def setExternalExtraJars(paths: java.util.ArrayList[String]): H2OConf = setExternalExtraJars(paths.asScala.toList)
 
   def setExternalExtraJars(paths: Seq[String]): H2OConf = setExternalExtraJars(paths.mkString(","))
 
diff --git a/core/src/main/scala/ai/h2o/sparkling/backend/utils/SupportedTypes.scala b/core/src/main/scala/ai/h2o/sparkling/backend/utils/SupportedTypes.scala
index 37ce8e4ac3..7f6149febc 100644
--- a/core/src/main/scala/ai/h2o/sparkling/backend/utils/SupportedTypes.scala
+++ b/core/src/main/scala/ai/h2o/sparkling/backend/utils/SupportedTypes.scala
@@ -23,6 +23,7 @@ import org.apache.spark.sql.types._
 import org.apache.spark.unsafe.types.UTF8String
 import water.fvec.Vec
 
+import scala.reflect.runtime.universe
 import scala.reflect.runtime.universe._
 
 /**
@@ -46,7 +47,7 @@ private[sparkling] object SupportedTypes extends Enumeration {
     def name: NameOfType = toString
   }
 
-  implicit val mirror = runtimeMirror(getClass.getClassLoader)
+  implicit val mirror: universe.Mirror = runtimeMirror(getClass.getClassLoader)
 
   def typeForClass[T](clazz: Class[T])(implicit runtimeMirror: Mirror) = runtimeMirror.classSymbol(clazz).toType
 
diff --git a/core/src/main/scala/org/apache/spark/h2o/backends/internal/InternalH2OBackend.scala b/core/src/main/scala/org/apache/spark/h2o/backends/internal/InternalH2OBackend.scala
index 7092f233aa..a8af3ce65d 100644
--- a/core/src/main/scala/org/apache/spark/h2o/backends/internal/InternalH2OBackend.scala
+++ b/core/src/main/scala/org/apache/spark/h2o/backends/internal/InternalH2OBackend.scala
@@ -24,7 +24,7 @@ import ai.h2o.sparkling.utils.SparkSessionUtils
 import ai.h2o.sparkling.{H2OConf, H2OContext}
 import org.apache.hadoop.conf.Configuration
 import org.apache.spark.expose.Utils
-import org.apache.spark.h2o.backends.internal.InternalH2OBackend._
+import org.apache.spark.h2o.backends.internal.InternalH2OBackend.{distributeFlatFile, getLeaderNode, lockCloud, registerEndpoints, registerNewExecutorListener, startH2OWorkers, startSingleH2OWorker, tearDownEndpoints, waitForClusterSize}
 import org.apache.spark.internal.Logging
 import org.apache.spark.rpc.RpcEndpointRef
 import org.apache.spark.scheduler.{SparkListener, SparkListenerExecutorAdded}
diff --git a/core/src/main/scala/org/apache/spark/h2o/backends/internal/SpreadRDDBuilder.scala b/core/src/main/scala/org/apache/spark/h2o/backends/internal/SpreadRDDBuilder.scala
index fd3e5051e9..867355182a 100644
--- a/core/src/main/scala/org/apache/spark/h2o/backends/internal/SpreadRDDBuilder.scala
+++ b/core/src/main/scala/org/apache/spark/h2o/backends/internal/SpreadRDDBuilder.scala
@@ -114,7 +114,7 @@ private[spark] class SpreadRDDBuilder(@transient private val hc: H2OContext, num
       val sb = sc.schedulerBackend
       sb match {
         case _: LocalSchedulerBackend => 1
-        case b: CoarseGrainedSchedulerBackend => b.getExecutorIds.length
+        case b: CoarseGrainedSchedulerBackend => b.getExecutorIds().length
         case _ => SparkEnv.get.blockManager.master.getStorageStatus.length - 1
       }
     }
diff --git a/gradle/scala.gradle b/gradle/scala.gradle
index 25aedb9f26..8dd11fbac9 100644
--- a/gradle/scala.gradle
+++ b/gradle/scala.gradle
@@ -27,7 +27,9 @@ configurations
         }
 
 dependencies {
-    scalaCompilerPlugin "org.scalamacros:paradise_${scalaVersion}:2.1.1"
+    if (scalaVersion < '2.13') {
+        scalaCompilerPlugin "org.scalamacros:paradise_${scalaVersion}:2.1.1"
+    }
 }
 
 // Activate Zinc compiler and configure scalac
diff --git a/ml/src/main/scala/ai/h2o/sparkling/ml/internals/H2OModel.scala b/ml/src/main/scala/ai/h2o/sparkling/ml/internals/H2OModel.scala
index fce9a18b94..847ebbc999 100644
--- a/ml/src/main/scala/ai/h2o/sparkling/ml/internals/H2OModel.scala
+++ b/ml/src/main/scala/ai/h2o/sparkling/ml/internals/H2OModel.scala
@@ -54,7 +54,7 @@ private[sparkling] class H2OModel private (val modelId: String) extends RestComm
 
   private[sparkling] def tryDelete(): Unit =
     try {
-      getCrossValidationModels.foreach(_.foreach(_.tryDelete()))
+      getCrossValidationModels().foreach(_.foreach(_.tryDelete()))
       delete()
     } catch {
       case e: Throwable => logWarning(s"Unsuccessful try to delete model '${this.modelId}'", e)
diff --git a/ml/src/main/scala/ai/h2o/sparkling/ml/models/H2OTargetEncoderModel.scala b/ml/src/main/scala/ai/h2o/sparkling/ml/models/H2OTargetEncoderModel.scala
index 23b8fa0eb8..32107a7264 100644
--- a/ml/src/main/scala/ai/h2o/sparkling/ml/models/H2OTargetEncoderModel.scala
+++ b/ml/src/main/scala/ai/h2o/sparkling/ml/models/H2OTargetEncoderModel.scala
@@ -67,7 +67,7 @@ class H2OTargetEncoderModel(override val uid: String, targetEncoderModel: Option
       val hc = H2OContext.ensure(
         "H2OContext needs to be created in order to use target encoding. Please create one as H2OContext.getOrCreate().")
       val temporaryColumn = getClass.getSimpleName + "_temporary_id"
-      val withIdDF = dataset.withColumn(temporaryColumn, monotonically_increasing_id)
+      val withIdDF = dataset.withColumn(temporaryColumn, monotonically_increasing_id())
       val flatDF = SchemaUtils.flattenDataFrame(withIdDF)
       val distinctInputCols = getInputCols().flatten.distinct
       val relevantColumns = distinctInputCols ++ Array(getLabelCol(), getFoldCol(), temporaryColumn).flatMap(Option(_))
diff --git a/ml/src/main/scala/ai/h2o/sparkling/ml/params/DictionaryParam.scala b/ml/src/main/scala/ai/h2o/sparkling/ml/params/DictionaryParam.scala
index d36a3d0715..82de10d14f 100644
--- a/ml/src/main/scala/ai/h2o/sparkling/ml/params/DictionaryParam.scala
+++ b/ml/src/main/scala/ai/h2o/sparkling/ml/params/DictionaryParam.scala
@@ -29,7 +29,7 @@ class DictionaryParam(parent: Params, name: String, doc: String, isValid: java.u
   def this(parent: Params, name: String, doc: String) =
     this(parent, name, doc, _ => true)
 
-  implicit def formats = DefaultFormats
+  implicit def formats: DefaultFormats.type = DefaultFormats
 
   override def jsonEncode(dictionary: java.util.Map[String, Double]): String = write(dictionary.asScala)
 
diff --git a/ml/src/main/scala/ai/h2o/sparkling/ml/params/HasLossByColNames.scala b/ml/src/main/scala/ai/h2o/sparkling/ml/params/HasLossByColNames.scala
index 5570d5e2ab..437c11d471 100644
--- a/ml/src/main/scala/ai/h2o/sparkling/ml/params/HasLossByColNames.scala
+++ b/ml/src/main/scala/ai/h2o/sparkling/ml/params/HasLossByColNames.scala
@@ -37,7 +37,7 @@ trait HasLossByColNames extends H2OAlgoParamsBase {
       null
     } else {
       val frameColumns = trainingFrame.columnNames
-      val indices = names.map(frameColumns.indexOf)
+      val indices = names.map(col => frameColumns.indexOf(col))
       indices
     }
 
diff --git a/ml/src/main/scala/ai/h2o/sparkling/ml/params/HasRandomCols.scala b/ml/src/main/scala/ai/h2o/sparkling/ml/params/HasRandomCols.scala
index 785f38adb8..cb000f90f9 100644
--- a/ml/src/main/scala/ai/h2o/sparkling/ml/params/HasRandomCols.scala
+++ b/ml/src/main/scala/ai/h2o/sparkling/ml/params/HasRandomCols.scala
@@ -35,7 +35,7 @@ trait HasRandomCols extends H2OAlgoParamsBase with H2OAlgoCommonUtils {
       null
     } else {
       val frameColumns = trainingFrame.columnNames
-      val indices = randomColumnNames.map(frameColumns.indexOf)
+      val indices = randomColumnNames.map(col => frameColumns.indexOf(col))
       indices
     }
 
diff --git a/ml/src/main/scala/ai/h2o/sparkling/ml/params/HyperParamsParam.scala b/ml/src/main/scala/ai/h2o/sparkling/ml/params/HyperParamsParam.scala
index 180e604b6d..8d6a17d1db 100644
--- a/ml/src/main/scala/ai/h2o/sparkling/ml/params/HyperParamsParam.scala
+++ b/ml/src/main/scala/ai/h2o/sparkling/ml/params/HyperParamsParam.scala
@@ -69,9 +69,9 @@ class HyperParamsParam(
       case JNull =>
         null
       case JArray(values) =>
-        val bytes = values.map {
+        val bytes: Array[Byte] = values.map {
           case JInt(x) =>
-            x.byteValue()
+            x.byteValue
           case _ =>
             throw new IllegalArgumentException(s"Cannot decode $json to Byte.")
         }.toArray
diff --git a/ml/src/main/scala/ai/h2o/sparkling/ml/params/NullableStringPairArrayParam.scala b/ml/src/main/scala/ai/h2o/sparkling/ml/params/NullableStringPairArrayParam.scala
index f428423a2f..cfa89bfb0c 100644
--- a/ml/src/main/scala/ai/h2o/sparkling/ml/params/NullableStringPairArrayParam.scala
+++ b/ml/src/main/scala/ai/h2o/sparkling/ml/params/NullableStringPairArrayParam.scala
@@ -56,9 +56,9 @@ class NullableStringPairArrayParam(
       case JNull =>
         null
       case JArray(values) =>
-        val bytes = values.map {
+        val bytes: Array[Byte] = values.map {
           case JInt(x) =>
-            x.byteValue()
+            x.byteValue
           case _ =>
             throw new IllegalArgumentException(s"Cannot decode $json to Byte.")
         }.toArray
diff --git a/scoring/src/main/scala/ai/h2o/sparkling/ml/models/H2OMOJOFlattenedInput.scala b/scoring/src/main/scala/ai/h2o/sparkling/ml/models/H2OMOJOFlattenedInput.scala
index c012ecd865..ed8599e925 100644
--- a/scoring/src/main/scala/ai/h2o/sparkling/ml/models/H2OMOJOFlattenedInput.scala
+++ b/scoring/src/main/scala/ai/h2o/sparkling/ml/models/H2OMOJOFlattenedInput.scala
@@ -78,6 +78,6 @@ trait H2OMOJOFlattenedInput {
     val relevantColumnNames = getRelevantColumnNames(flatDataFrame, inputs)
     val args = relevantColumnNames.map(c => flatDataFrame(s"`$c`"))
     val udf = udfConstructor(relevantColumnNames)
-    flatDataFrame.withColumn(outputColumnName, udf(struct(args: _*)))
+    flatDataFrame.withColumn(outputColumnName, udf(struct(args.toIndexedSeq: _*)))
   }
 }
diff --git a/scoring/src/main/scala/ai/h2o/sparkling/ml/models/H2OMOJOModel.scala b/scoring/src/main/scala/ai/h2o/sparkling/ml/models/H2OMOJOModel.scala
index cb734844e3..8984a1abcc 100644
--- a/scoring/src/main/scala/ai/h2o/sparkling/ml/models/H2OMOJOModel.scala
+++ b/scoring/src/main/scala/ai/h2o/sparkling/ml/models/H2OMOJOModel.scala
@@ -282,9 +282,9 @@ abstract class H2OMOJOModel
         // Propagation of offset to EasyPredictModelWrapper was introduced with H2OSupervisedMOJOModel.
         // `lit(0.0)` represents a column with zero values (offset disabled) to ensure backward-compatibility of
         // MOJO models.
-        flatDataFrame.withColumn(outputColumnName, udf(struct(args: _*), lit(0.0)))
+        flatDataFrame.withColumn(outputColumnName, udf(struct(args.toIndexedSeq: _*), lit(0.0)))
       case _ =>
-        flatDataFrame.withColumn(outputColumnName, udf(struct(args: _*)))
+        flatDataFrame.withColumn(outputColumnName, udf(struct(args.toIndexedSeq: _*)))
     }
   }
 
diff --git a/scoring/src/main/scala/ai/h2o/sparkling/ml/models/H2OSupervisedMOJOModel.scala b/scoring/src/main/scala/ai/h2o/sparkling/ml/models/H2OSupervisedMOJOModel.scala
index 38af0a18dc..ff369c840f 100644
--- a/scoring/src/main/scala/ai/h2o/sparkling/ml/models/H2OSupervisedMOJOModel.scala
+++ b/scoring/src/main/scala/ai/h2o/sparkling/ml/models/H2OSupervisedMOJOModel.scala
@@ -57,14 +57,16 @@ class H2OSupervisedMOJOModel(override val uid: String) extends H2OAlgorithmMOJOM
           if (!flatDataFrame.columns.contains(offsetColumn)) {
             throw new RuntimeException("Offset column must be present within the dataset!")
           }
-          flatDataFrame.withColumn(outputColumnName, udf(struct(args: _*), col(getOffsetCol()).cast(DoubleType)))
+          flatDataFrame.withColumn(
+            outputColumnName,
+            udf(struct(args.toIndexedSeq: _*), col(getOffsetCol()).cast(DoubleType)))
         } else {
           // Methods of EasyPredictModelWrapper for given prediction categories take offset as parameter.
           // `lit(0.0)` represents a column with zero values (offset disabled).
-          flatDataFrame.withColumn(outputColumnName, udf(struct(args: _*), lit(0.0)))
+          flatDataFrame.withColumn(outputColumnName, udf(struct(args.toIndexedSeq: _*), lit(0.0)))
         }
       case _ =>
-        flatDataFrame.withColumn(outputColumnName, udf(struct(args: _*)))
+        flatDataFrame.withColumn(outputColumnName, udf(struct(args.toIndexedSeq: _*)))
     }
   }
 }
diff --git a/scoring/src/main/scala/ai/h2o/sparkling/ml/models/H2OTargetEncoderBase.scala b/scoring/src/main/scala/ai/h2o/sparkling/ml/models/H2OTargetEncoderBase.scala
index f41e811b58..08aaa71e79 100644
--- a/scoring/src/main/scala/ai/h2o/sparkling/ml/models/H2OTargetEncoderBase.scala
+++ b/scoring/src/main/scala/ai/h2o/sparkling/ml/models/H2OTargetEncoderBase.scala
@@ -74,6 +74,6 @@ trait H2OTargetEncoderBase extends PipelineStage with H2OTargetEncoderMOJOParams
 
   private[sparkling] def createVectorColumn(df: DataFrame, name: String, sourceColumns: Array[String]): DataFrame = {
     val assembler = new VectorAssembler().setInputCols(sourceColumns).setOutputCol(name)
-    assembler.transform(df).drop(sourceColumns: _*)
+    assembler.transform(df).drop(sourceColumns.toIndexedSeq: _*)
   }
 }
diff --git a/scoring/src/main/scala/ai/h2o/sparkling/ml/models/H2OTargetEncoderMOJOModel.scala b/scoring/src/main/scala/ai/h2o/sparkling/ml/models/H2OTargetEncoderMOJOModel.scala
index 08149d2eae..9c7a8d6b49 100644
--- a/scoring/src/main/scala/ai/h2o/sparkling/ml/models/H2OTargetEncoderMOJOModel.scala
+++ b/scoring/src/main/scala/ai/h2o/sparkling/ml/models/H2OTargetEncoderMOJOModel.scala
@@ -98,7 +98,8 @@ case class H2OTargetEncoderMOJOUdfWrapper(
     new EasyPredictModelWrapper(config)
   }
 
-  @transient private lazy val positions: Seq[Int] = mojoModel._inoutMapping.asScala.map(_.to.length).scanLeft(0)(_ + _)
+  @transient private lazy val positions: Seq[Int] =
+    mojoModel._inoutMapping.asScala.map(_.to.length).scanLeft(0)(_ + _).toSeq
 
   val mojoUdf: UserDefinedFunction =
     udf[Array[Option[Vector]], Row] { r: Row =>
diff --git a/scoring/src/main/scala/ai/h2o/sparkling/ml/params/NullableStringArrayArrayParam.scala b/scoring/src/main/scala/ai/h2o/sparkling/ml/params/NullableStringArrayArrayParam.scala
index d6a12c1cf8..07debcde86 100644
--- a/scoring/src/main/scala/ai/h2o/sparkling/ml/params/NullableStringArrayArrayParam.scala
+++ b/scoring/src/main/scala/ai/h2o/sparkling/ml/params/NullableStringArrayArrayParam.scala
@@ -53,9 +53,9 @@ class NullableStringArrayArrayParam(parent: Params, name: String, doc: String, i
       case JNull =>
         null
       case JArray(values) =>
-        val bytes = values.map {
+        val bytes: Array[Byte] = values.map {
           case JInt(x) =>
-            x.byteValue()
+            x.byteValue
           case _ =>
             throw new IllegalArgumentException(s"Cannot decode $json to Byte.")
         }.toArray
diff --git a/scoring/src/main/scala/ai/h2o/sparkling/ml/params/NullableStringPairArrayParam.scala b/scoring/src/main/scala/ai/h2o/sparkling/ml/params/NullableStringPairArrayParam.scala
index f4306557e4..b2ed5f1cbf 100644
--- a/scoring/src/main/scala/ai/h2o/sparkling/ml/params/NullableStringPairArrayParam.scala
+++ b/scoring/src/main/scala/ai/h2o/sparkling/ml/params/NullableStringPairArrayParam.scala
@@ -57,9 +57,9 @@ class NullableStringPairArrayParam(
       case JNull =>
         null
       case JArray(values) =>
-        val bytes = values.map {
+        val bytes: Array[Byte] = values.map {
           case JInt(x) =>
-            x.byteValue()
+            x.byteValue
           case _ =>
             throw new IllegalArgumentException(s"Cannot decode $json to Byte.")
         }.toArray
diff --git a/utils/src/main/scala/ai/h2o/sparkling/ml/utils/SchemaUtils.scala b/utils/src/main/scala/ai/h2o/sparkling/ml/utils/SchemaUtils.scala
index 87815bdd3d..9c9a6faf03 100644
--- a/utils/src/main/scala/ai/h2o/sparkling/ml/utils/SchemaUtils.scala
+++ b/utils/src/main/scala/ai/h2o/sparkling/ml/utils/SchemaUtils.scala
@@ -143,7 +143,7 @@ object SchemaUtils {
 
   def flattenSchema(df: DataFrame): StructType = {
     val rowSchemas = rowsToRowSchemas(df)
-    val mergedSchema = mergeRowSchemas(rowSchemas)
+    val mergedSchema = mergeRowSchemas(rowSchemas).toList
     StructType(mergedSchema.map(_.field))
   }
 
@@ -221,13 +221,13 @@ object SchemaUtils {
     if (data != null) {
       dataType match {
         case BinaryType =>
-          flattenBinaryType(qualifiedName, ByteType, nullable, metadata, data, path)
+          flattenBinaryType(qualifiedName, ByteType, nullable, metadata, data, path).toList
         case MapType(_, valueType, containsNull) =>
-          flattenMapType(qualifiedName, valueType, containsNull || nullable, metadata, data, path)
+          flattenMapType(qualifiedName, valueType, containsNull || nullable, metadata, data, path).toList
         case ArrayType(elementType, containsNull) =>
-          flattenArrayType(qualifiedName, elementType, containsNull || nullable, metadata, data, path)
+          flattenArrayType(qualifiedName, elementType, containsNull || nullable, metadata, data, path).toList
         case StructType(fields) =>
-          flattenStructType(qualifiedName, nullable, metadata, fields, data, path)
+          flattenStructType(qualifiedName, nullable, metadata, fields, data, path).toList
         case dt =>
           FieldWithOrder(StructField(qualifiedName, dt, nullable, metadata), path.reverse) :: Nil
       }
@@ -317,7 +317,7 @@ object SchemaUtils {
       targetColPrefix: Option[String] = None,
       nullable: Boolean = false): Seq[(StructField, String)] = {
 
-    val flattened = schema.fields.flatMap { f =>
+    val flattened = schema.fields.toList.flatMap { f =>
       val escaped = if (f.name.contains(".")) "`" + f.name + "`" else f.name
       val colName = if (sourceColPrefix.isDefined) sourceColPrefix.get + "." + escaped else escaped
       val newName = if (targetColPrefix.isDefined) targetColPrefix.get + "." + f.name else f.name
@@ -402,7 +402,7 @@ object SchemaUtils {
           getCollectionSize(row, idx)
         }
       }
-      if (sizes.isEmpty) {
+      if (sizes.isEmpty()) {
         Array(0)
       } else {
         sizes.reduce((a, b) => a.indices.map(i => if (a(i) > b(i)) a(i) else b(i))).toArray
diff --git a/utils/src/main/scala/ai/h2o/sparkling/utils/SparkSessionUtils.scala b/utils/src/main/scala/ai/h2o/sparkling/utils/SparkSessionUtils.scala
index 6409ffec8b..8d1cf6e529 100644
--- a/utils/src/main/scala/ai/h2o/sparkling/utils/SparkSessionUtils.scala
+++ b/utils/src/main/scala/ai/h2o/sparkling/utils/SparkSessionUtils.scala
@@ -35,7 +35,7 @@ object SparkSessionUtils extends Logging {
   }
 
   def createSparkSession(conf: SparkConf, forceHive: Boolean = false): SparkSession = {
-    val builder = SparkSession.builder.config(conf)
+    val builder = SparkSession.builder().config(conf)
     if (conf.get(CATALOG_IMPLEMENTATION.key, "hive").toLowerCase == "hive" || forceHive) {
       if (ExposeUtils.hiveClassesArePresent || forceHive) {
         builder.enableHiveSupport()