fix: Fix issue with MCP tools throwing an error

Fixes: #3082
PiperOrigin-RevId: 824620839

Author: google-genai-bot

src/google/adk/tools/_gemini_schema_util.py

@@ -75,27 +75,29 @@ def _to_snake_case(text: str) -> str:
 
 
 def _sanitize_schema_type(schema: dict[str, Any]) -> dict[str, Any]:
-  if ("type" not in schema or not schema["type"]) and schema.keys().isdisjoint(
-      schema
-  ):
+  if not schema:
     schema["type"] = "object"
   if isinstance(schema.get("type"), list):
-    nullable = False
-    non_null_type = None
-    for t in schema["type"]:
-      if t == "null":
-        nullable = True
-      elif not non_null_type:
-        non_null_type = t
-    if not non_null_type:
-      non_null_type = "object"
+    types_no_null = [t for t in schema["type"] if t != "null"]
+    nullable = len(types_no_null) != len(schema["type"])
+    if "array" in types_no_null:
+      non_null_type = "array"
+    else:
+      non_null_type = types_no_null[0] if types_no_null else "object"
     if nullable:
       schema["type"] = [non_null_type, "null"]
     else:
       schema["type"] = non_null_type
   elif schema.get("type") == "null":
     schema["type"] = ["object", "null"]
 
+  schema_type = schema.get("type")
+  is_array = schema_type == "array" or (
+      isinstance(schema_type, list) and "array" in schema_type
+  )
+  if is_array and "items" not in schema:
+    schema["items"] = {"type": "string"}
+
   return schema
 
 

tests/unittests/tools/test_gemini_schema_util.py

@@ -68,6 +68,11 @@ def test_to_gemini_schema_array_string_types(self):
             "object_nullable": {"type": "null"},
             "multi_types_nullable": {"type": ["string", "null", "integer"]},
             "empty_default_object": {},
+            "empty_list_type": {"type": []},
+            "multi_type_with_array_nullable": {
+                "type": ["string", "array", "null"]
+            },
+            "multi_type_with_array_nonnullable": {"type": ["integer", "array"]},
         },
     }
     gemini_schema = _to_gemini_schema(openapi_schema)
@@ -93,6 +98,23 @@ def test_to_gemini_schema_array_string_types(self):
     assert gemini_schema.properties["empty_default_object"].type == Type.OBJECT
     assert gemini_schema.properties["empty_default_object"].nullable is None
 
+    assert gemini_schema.properties["empty_list_type"].type == Type.OBJECT
+    assert not gemini_schema.properties["empty_list_type"].nullable
+
+    assert (
+        gemini_schema.properties["multi_type_with_array_nullable"].type
+        == Type.ARRAY
+    )
+    assert gemini_schema.properties["multi_type_with_array_nullable"].nullable
+
+    assert (
+        gemini_schema.properties["multi_type_with_array_nonnullable"].type
+        == Type.ARRAY
+    )
+    assert not gemini_schema.properties[
+        "multi_type_with_array_nonnullable"
+    ].nullable
+
   def test_to_gemini_schema_nested_objects(self):
     openapi_schema = {
         "type": "object",
@@ -137,6 +159,20 @@ def test_to_gemini_schema_nested_array(self):
     gemini_schema = _to_gemini_schema(openapi_schema)
     assert gemini_schema.items.properties["name"].type == Type.STRING
 
+  def test_to_gemini_schema_array_without_items_gets_default(self):
+    openapi_schema = {"type": "array"}
+    gemini_schema = _to_gemini_schema(openapi_schema)
+    assert gemini_schema.type == Type.ARRAY
+    assert not gemini_schema.nullable
+    assert gemini_schema.items.type == Type.STRING
+
+  def test_to_gemini_schema_nullable_array_without_items_gets_default(self):
+    openapi_schema = {"type": ["array", "null"]}
+    gemini_schema = _to_gemini_schema(openapi_schema)
+    assert gemini_schema.type == Type.ARRAY
+    assert gemini_schema.nullable
+    assert gemini_schema.items.type == Type.STRING
+
   def test_to_gemini_schema_any_of(self):
     openapi_schema = {
         "anyOf": [{"type": "string"}, {"type": "integer"}],
@@ -533,8 +569,10 @@ def test_sanitize_schema_formats_for_gemini_nullable(self):
                 "type": "string",
             },
             "next_page_token": {
-                "anyOf": [{"type": "string"}, {"type": "null"}],
-                "default": None,
+                "any_of": [
+                    {"type": "string"},
+                    {"type": ["object", "null"]},
+                ],
                 "description": (
                     "The nextPageToken to fetch the next page of results."
                 ),