fix: knowledge retrieval validation error (#22682)

api/core/workflow/nodes/knowledge_retrieval/entities.py

     multiple_retrieval_config: Optional[MultipleRetrievalConfig] = None
     single_retrieval_config: Optional[SingleRetrievalConfig] = None
     metadata_filtering_mode: Optional[Literal["disabled", "automatic", "manual"]] = "disabled"
-    metadata_model_config: ModelConfig
+    metadata_model_config: Optional[ModelConfig] = None
     metadata_filtering_conditions: Optional[MetadataFilteringCondition] = None
     vision: VisionConfig = Field(default_factory=VisionConfig)
 

api/core/workflow/nodes/knowledge_retrieval/knowledge_retrieval_node.py

         # get all metadata field
         metadata_fields = db.session.query(DatasetMetadata).filter(DatasetMetadata.dataset_id.in_(dataset_ids)).all()
         all_metadata_fields = [metadata_field.name for metadata_field in metadata_fields]
+        if node_data.metadata_model_config is None:
+            raise ValueError("metadata_model_config is required")
         # get metadata model instance and fetch model config
         model_instance, model_config = self.get_model_config(node_data.metadata_model_config)
         # fetch prompt messages
         )
 
     def _get_prompt_template(self, node_data: KnowledgeRetrievalNodeData, metadata_fields: list, query: str):
-        model_mode = ModelMode(node_data.metadata_model_config.mode)
+        model_mode = ModelMode(node_data.metadata_model_config.mode)  # type: ignore
         input_text = query
 
         prompt_messages: list[LLMNodeChatModelMessage] = []