diff --git a/l2p/domain_builder.py b/l2p/domain_builder.py
index 3d6d893..310094c 100644
--- a/l2p/domain_builder.py
+++ b/l2p/domain_builder.py
@@ -289,32 +289,28 @@ def extract_pddl_action(
                                     llm_response, syntax_validator.unsupported_keywords
                                 )
                             )
-                        elif e == "invalid_param_types":
+                        elif e == "invalid_param_types" and types:
                             validation_info = syntax_validator.validate_params(
                                 action["params"], types
                             )
-                        elif e == "invalid_predicate_name":
+                        elif e == "invalid_predicate_name" and types:
                             validation_info = (
                                 syntax_validator.validate_types_predicates(
                                     new_predicates, types
                                 )
                             )
-                        elif e == "invalid_predicate_format":
+                        elif e == "invalid_predicate_format" and types:
                             validation_info = (
                                 syntax_validator.validate_format_predicates(
                                     predicates, types
                                 )
                             )
-                        elif e == "invalid_predicate_usage":
+                        elif e == "invalid_predicate_usage" and types:
                             validation_info = (
                                 syntax_validator.validate_usage_predicates(
                                     llm_response, predicates, types
                                 )
                             )
-                        else:
-                            raise NotImplementedError(
-                                f"Validation type '{e}' is not implemented."
-                            )
 
                         if not validation_info[0]:
                             return action, new_predicates, llm_response, validation_info
@@ -759,7 +755,7 @@ def get_predicates(self):
     def generate_domain(
         self,
         domain: str,
-        types: str,
+        types: str | None,
         predicates: str,
         actions: list[Action],
         requirements: list[str],
@@ -783,7 +779,8 @@ def generate_domain(
             indent(string=f"(:requirements\n   {' '.join(requirements)})", level=1)
             + "\n\n"
         )
-        desc += f"   (:types \n{indent(string=types, level=2)}\n   )\n\n"
+        if types:  # Only add types if not None or empty string
+            desc += f"   (:types \n{indent(string=types, level=2)}\n   )\n\n"
         desc += f"   (:predicates \n{indent(string=predicates, level=2)}\n   )"
         desc += self.action_descs(actions)
         desc += "\n)"
diff --git a/l2p/llm_builder.py b/l2p/llm_builder.py
index c30d0fa..2672dfa 100644
--- a/l2p/llm_builder.py
+++ b/l2p/llm_builder.py
@@ -258,6 +258,8 @@ def valid_models(self) -> list[str]:
             "gpt-4-32k",
             "gpt-4o",
             "gpt-4o-mini",
+            "o1",
+            "o3-mini"
         ]
 
 
diff --git a/l2p/utils/pddl_validator.py b/l2p/utils/pddl_validator.py
index b8257fc..a419401 100644
--- a/l2p/utils/pddl_validator.py
+++ b/l2p/utils/pddl_validator.py
@@ -37,12 +37,27 @@ def __init__(self, error_types=None, unsupported_keywords=None):
     # PARAMETER CHECKS
 
     def validate_params(
-        self, parameters: OrderedDict, types: dict[str, str]
+        self, parameters: OrderedDict, types: dict[str, str] | None
     ) -> tuple[bool, str]:
         """Checks whether a PDDL action parameter contains types found in object types."""
+        
+        types = types or {}
+        
+        # If no types are defined, inform the user and check for parameter types
+        if not types:
+            for param_name, param_type in parameters.items():
+                if param_type is not None and param_type != "":
+                    feedback_msg = (
+                        f'The parameter `{param_name}` has an object type `{param_type}` '
+                        'while no types are defined. Please remove the object type from this parameter.'
+                    )
+                    return False, feedback_msg
+            
+            # if all parameter names do not contain a type
+            return True, "PASS: All parameters are valid."
 
-        for param_name in parameters:
-            param_type = parameters[param_name]
+        # Otherwise, check that parameter types are valid in the given types
+        for param_name, param_type in parameters.items():
 
             if not any(param_type in t for t in types.keys()):
                 feedback_msg = f'There is an invalid object type `{param_type}` for the parameter {param_name} not found in the types {types.keys()}. If you need to use a new type, you can emulate it with an "is_{{type}} ?o - object" precondition. Please revise the PDDL model to fix this error.'
@@ -54,9 +69,16 @@ def validate_params(
     # PREDICATE CHECKS
 
     def validate_types_predicates(
-        self, predicates: list[dict], types: dict[str, str]
+        self, predicates: list[dict], types: dict[str, str] | None
     ) -> tuple[bool, str]:
         """Check if predicate name is found within any type definitions"""
+        
+        # Handle the case where types is None or empty
+        types = types or {}
+        
+        if not types:
+            feedback_msg = "PASS: All predicate names are unique to object type names"
+            return True, feedback_msg
 
         invalid_predicates = list()
         for pred in predicates: