fix: Fix issue with MCP tools throwing an error.

The error "parameters.properties[segmentation_classes].items: missing
field" indicates _to_gemini_schema isn't correctly
handling array types.

Author: nickvander

src/google/adk/tools/_gemini_schema_util.py

@@ -89,16 +89,19 @@ def _sanitize_schema_type(schema: dict[str, Any]) -> dict[str, Any]:
         non_null_type = t
     if not non_null_type:
       non_null_type = "object"
+    if non_null_type == "array" and "items" not in schema:
+      schema["items"] = {"type": "string"}
     if nullable:
       schema["type"] = [non_null_type, "null"]
     else:
       schema["type"] = non_null_type
   elif schema.get("type") == "null":
     schema["type"] = ["object", "null"]
+  elif schema.get("type") == "array" and "items" not in schema:
+    schema["items"] = {"type": "string"}
 
   return schema
 
-
 def _dereference_schema(schema: dict[str, Any]) -> dict[str, Any]:
   """Resolves $ref pointers in a JSON schema."""