fix(api-nodes-nanobana): raise error when not output image is present (Comfy-Org#13167)

Signed-off-by: bigcat88 <bigcat88@icloud.com>

Author: bigcat88

comfy_api_nodes/nodes_gemini.py

@@ -201,6 +201,16 @@ async def get_image_from_response(response: GeminiGenerateContentResponse, thoug
             returned_image = await download_url_to_image_tensor(part.fileData.fileUri)
         image_tensors.append(returned_image)
     if len(image_tensors) == 0:
+        if not thought:
+            # No images generated --> extract text response for a meaningful error
+            model_message = get_text_from_response(response).strip()
+            if model_message:
+                raise ValueError(f"Gemini did not generate an image. Model response: {model_message}")
+            raise ValueError(
+                "Gemini did not generate an image. "
+                "Try rephrasing your prompt or changing the response modality to 'IMAGE+TEXT' "
+                "to see the model's reasoning."
+            )
         return torch.zeros((1, 1024, 1024, 4))
     return torch.cat(image_tensors, dim=0)