fix: allow empty content for TextPart on GoogleModel (#2203)

Author: caesarnine

pydantic_ai_slim/pydantic_ai/models/google.py

@@ -484,8 +484,7 @@ def _content_model_response(m: ModelResponse) -> ContentDict:
             function_call = FunctionCallDict(name=item.tool_name, args=item.args_as_dict(), id=item.tool_call_id)
             parts.append({'function_call': function_call})
         elif isinstance(item, TextPart):
-            if item.content:  # pragma: no branch
-                parts.append({'text': item.content})
+            parts.append({'text': item.content})
         elif isinstance(item, ThinkingPart):  # pragma: no cover
             # NOTE: We don't send ThinkingPart to the providers yet. If you are unsatisfied with this,
             # please open an issue. The below code is the code to send thinking to the provider.

tests/models/cassettes/test_google/test_google_model_empty_assistant_response.yaml

@@ -0,0 +1,60 @@
+interactions:
+- request:
+    headers:
+      content-type:
+      - application/json
+    method: post
+    parsed_body:
+      contents:
+      - parts:
+        - text: Hi
+        role: user
+      - parts:
+        - text: ''
+        role: model
+      - parts:
+        - text: Empty?
+        role: user
+      generationConfig: {}
+    uri: https://generativelanguage.googleapis.com/v1beta/models/gemini-1.5-flash:generateContent
+  response:
+    headers:
+      alt-svc:
+      - h3=":443"; ma=2592000,h3-29=":443"; ma=2592000
+      content-length:
+      - '724'
+      content-type:
+      - application/json; charset=UTF-8
+      server-timing:
+      - gfet4t7; dur=387
+      transfer-encoding:
+      - chunked
+      vary:
+      - Origin
+      - X-Origin
+      - Referer
+    parsed_body:
+      candidates:
+      - avgLogprobs: -0.02701732359434429
+        content:
+          parts:
+          - text: |
+              Yes, your previous message was empty.  Is there anything I can help you with?
+          role: model
+        finishReason: STOP
+      modelVersion: gemini-1.5-flash
+      responseId: NHt4aPycNfzcnvgP1q6EgQw
+      usageMetadata:
+        candidatesTokenCount: 19
+        candidatesTokensDetails:
+        - modality: TEXT
+          tokenCount: 19
+        promptTokenCount: 3
+        promptTokensDetails:
+        - modality: TEXT
+          tokenCount: 3
+        totalTokenCount: 22
+    status:
+      code: 200
+      message: OK
+version: 1

tests/models/test_google.py

@@ -604,6 +604,21 @@ async def test_google_model_empty_user_prompt(allow_model_requests: None, google
     assert result.output == snapshot("I'm ready to assist you.  Please tell me what you need.\n")
 
 
+async def test_google_model_empty_assistant_response(allow_model_requests: None, google_provider: GoogleProvider):
+    m = GoogleModel('gemini-1.5-flash', provider=google_provider)
+    agent = Agent(m)
+
+    result = await agent.run(
+        'Empty?',
+        message_history=[
+            ModelRequest(parts=[UserPromptPart(content='Hi')]),
+            ModelResponse(parts=[TextPart(content='')]),
+        ],
+    )
+
+    assert result.output == snapshot('Yes, your previous message was empty.  Is there anything I can help you with?\n')
+
+
 async def test_google_model_thinking_part(allow_model_requests: None, google_provider: GoogleProvider):
     m = GoogleModel('gemini-2.5-pro-preview-03-25', provider=google_provider)
     settings = GoogleModelSettings(google_thinking_config={'include_thoughts': True})