Fix: Handle empty/invalid JSON in client.chat.parse()

src/mistralai/extra/struct_chat.py

@@ -24,7 +24,17 @@ def convert_to_parsed_chat_completion_response(response: ChatCompletionResponse,
                     parsed=None
                 )
                 if isinstance(parsed_message.content, str):
-                    parsed_message.parsed = pydantic_model_from_json(json.loads(parsed_message.content), response_format)
+                    # Validate content is non-empty and valid JSON before parsing
+                    content = parsed_message.content.strip()
+                    if content:
+                        try:
+                            parsed_message.parsed = pydantic_model_from_json(json.loads(content), response_format)
+                        except json.JSONDecodeError:
+                            # Handle invalid JSON gracefully - treat as unparseable content
+                            parsed_message.parsed = None
+                    else:
+                        # Empty or whitespace-only content
+                        parsed_message.parsed = None
                 elif parsed_message.content is None:
                     parsed_message.parsed = None
                 else:

src/mistralai/extra/tests/test_struct_chat.py

@@ -98,6 +98,117 @@ def test_convert_to_parsed_chat_completion_response(self):
         )
         self.assertEqual(output, expected_response)
 
+    def test_empty_string_content(self):
+        """Test that empty string content is handled gracefully (issue #282)"""
+        response = ChatCompletionResponse(
+            id="test-empty",
+            object="chat.completion",
+            model="codestral-latest",
+            usage=UsageInfo(prompt_tokens=10, completion_tokens=0, total_tokens=10),
+            created=1234567890,
+            choices=[
+                ChatCompletionChoice(
+                    index=0,
+                    message=AssistantMessage(
+                        content="",  # Empty string
+                        tool_calls=None,
+                        prefix=False,
+                        role="assistant",
+                    ),
+                    finish_reason="stop",
+                )
+            ],
+        )
+
+        # Should not raise JSONDecodeError
+        result = convert_to_parsed_chat_completion_response(response, MathDemonstration)
+        self.assertIsNotNone(result)
+        self.assertEqual(len(result.choices), 1)
+        self.assertIsNone(result.choices[0].message.parsed)
+
+    def test_whitespace_only_content(self):
+        """Test that whitespace-only content is handled gracefully (issue #282)"""
+        response = ChatCompletionResponse(
+            id="test-whitespace",
+            object="chat.completion",
+            model="codestral-latest",
+            usage=UsageInfo(prompt_tokens=10, completion_tokens=0, total_tokens=10),
+            created=1234567890,
+            choices=[
+                ChatCompletionChoice(
+                    index=0,
+                    message=AssistantMessage(
+                        content="   ",  # Whitespace only
+                        tool_calls=None,
+                        prefix=False,
+                        role="assistant",
+                    ),
+                    finish_reason="stop",
+                )
+            ],
+        )
+
+        # Should not raise JSONDecodeError
+        result = convert_to_parsed_chat_completion_response(response, MathDemonstration)
+        self.assertIsNotNone(result)
+        self.assertEqual(len(result.choices), 1)
+        self.assertIsNone(result.choices[0].message.parsed)
+
+    def test_invalid_json_content(self):
+        """Test that invalid JSON content is handled gracefully (issue #282)"""
+        response = ChatCompletionResponse(
+            id="test-invalid-json",
+            object="chat.completion",
+            model="codestral-latest",
+            usage=UsageInfo(prompt_tokens=10, completion_tokens=20, total_tokens=30),
+            created=1234567890,
+            choices=[
+                ChatCompletionChoice(
+                    index=0,
+                    message=AssistantMessage(
+                        content="This is not JSON at all",  # Invalid JSON
+                        tool_calls=None,
+                        prefix=False,
+                        role="assistant",
+                    ),
+                    finish_reason="stop",
+                )
+            ],
+        )
+
+        # Should not raise JSONDecodeError
+        result = convert_to_parsed_chat_completion_response(response, MathDemonstration)
+        self.assertIsNotNone(result)
+        self.assertEqual(len(result.choices), 1)
+        self.assertIsNone(result.choices[0].message.parsed)
+
+    def test_none_content(self):
+        """Test that None content is handled correctly"""
+        response = ChatCompletionResponse(
+            id="test-none",
+            object="chat.completion",
+            model="codestral-latest",
+            usage=UsageInfo(prompt_tokens=10, completion_tokens=0, total_tokens=10),
+            created=1234567890,
+            choices=[
+                ChatCompletionChoice(
+                    index=0,
+                    message=AssistantMessage(
+                        content=None,  # None
+                        tool_calls=None,
+                        prefix=False,
+                        role="assistant",
+                    ),
+                    finish_reason="stop",
+                )
+            ],
+        )
+
+        result = convert_to_parsed_chat_completion_response(response, MathDemonstration)
+        self.assertIsNotNone(result)
+        self.assertEqual(len(result.choices), 1)
+        self.assertIsNone(result.choices[0].message.parsed)
+
 
 if __name__ == "__main__":
     unittest.main()