fixes Cannot take a Union of no types.

Fixes #71

src/mcpadapt/utils/modeling.py

@@ -132,7 +132,12 @@ def get_field_type(field_name: str, field_schema: Dict[str, Any], required: set)
 
                     types.append(created_models[ref_name])
 
-            field_type = types[0] if len(types) == 1 else Union[tuple(types)]  # type: ignore
+            if len(types) == 0:
+                field_type = Any
+            elif len(types) == 1:
+                field_type = types[0]
+            else:
+                field_type = Union[tuple(types)]  # type: ignore
             default = field_schema.get("default")
             is_required = field_name in required and default is None
 
@@ -158,10 +163,12 @@ def get_field_type(field_name: str, field_schema: Dict[str, Any], required: set)
                         mapped_type = json_type_mapping.get(t, Any)
                         types.append(mapped_type)
 
-                if len(types) > 1:
-                    field_type = Union[tuple(types)]  # type: ignore
+                if len(types) == 0:
+                    field_type = Any
+                elif len(types) == 1:
+                    field_type = types[0]
                 else:
-                    field_type = types[0] if types else Any
+                    field_type = Union[tuple(types)]  # type: ignore
             else:
                 # Original code for simple types
                 field_type = json_type_mapping.get(json_type, Any)  # type: ignore

tests/test_crewai_adapter.py

@@ -482,9 +482,9 @@ async def arun():
 
 
 def test_empty_union_type_error(empty_union_server_script):
-    """Test that empty unions (anyOf with only null types) raise TypeError.
+    """Test that empty unions (anyOf with only null types) do not raise TypeError.
 
-    This test reproduces issue #71 where schemas with anyOf containing only
+    This test reproduced issue #71 where schemas with anyOf containing only
     null types cause 'Cannot take a Union of no types' error.
     """
     with MCPAdapt(
@@ -494,5 +494,4 @@ def test_empty_union_type_error(empty_union_server_script):
         ),
         CrewAIAdapter(),
     ) as tools:
-        # Should raise TypeError before reaching here
-        pass
+        assert len(tools) == 1