fix: handle optional content types in LLM response parsing

- Add get_text_content() helper method to PromptMessage class
- Update generate_suggested_questions_after_answer to use the helper method
- Properly handle str, list[PromptMessageContent], and None content types

api/core/llm_generator/llm_generator.py

@@ -114,7 +114,8 @@ class LLMGenerator:
                 ),
             )
 
-            questions = output_parser.parse(cast(str, response.message.content))
+            text_content = response.message.get_text_content()
+            questions = output_parser.parse(text_content) if text_content else []
         except InvokeError:
             questions = []
         except Exception:

api/core/llm_generator/output_parser/suggested_questions_after_answer.py

@@ -10,9 +10,6 @@ class SuggestedQuestionsAfterAnswerOutputParser:
         return SUGGESTED_QUESTIONS_AFTER_ANSWER_INSTRUCTION_PROMPT
 
     def parse(self, text: str) -> Any:
-        if not isinstance(text, str):
-            # Optionally log a warning here
-            return []
         action_match = re.search(r"\[.*?\]", text.strip(), re.DOTALL)
         if action_match is not None:
             json_obj = json.loads(action_match.group(0).strip())

api/core/model_runtime/entities/message_entities.py

@@ -156,6 +156,23 @@ class PromptMessage(ABC, BaseModel):
         """
         return not self.content
 
+    def get_text_content(self) -> str:
+        """
+        Get text content from prompt message.
+
+        :return: Text content as string, empty string if no text content
+        """
+        if isinstance(self.content, str):
+            return self.content
+        elif isinstance(self.content, list):
+            text_parts = []
+            for item in self.content:
+                if isinstance(item, TextPromptMessageContent):
+                    text_parts.append(item.data)
+            return "".join(text_parts)
+        else:
+            return ""
+
     @field_validator("content", mode="before")
     @classmethod
     def validate_content(cls, v):