fix: prevent SQL errors when metadata filter Constant value is None or blank

- Added early check in  to skip filters where value is None
- Updated both  and  for consistent handling
- Prevents type cast errors when users leave metadata filter values blank in Chatflow apps

Fixes #21800

api/core/rag/retrieval/dataset_retrieval.py

@@ -1010,6 +1010,9 @@ class DatasetRetrieval:
     def _process_metadata_filter_func(
         self, sequence: int, condition: str, metadata_name: str, value: Optional[Any], filters: list
     ):
+        if value is None:
+            return
+
         key = f"{metadata_name}_{sequence}"
         key_value = f"{metadata_name}_{sequence}_value"
         match condition:

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

@@ -490,6 +490,9 @@ class KnowledgeRetrievalNode(LLMNode):
     def _process_metadata_filter_func(
         self, sequence: int, condition: str, metadata_name: str, value: Optional[Any], filters: list
     ):
+        if value is None:
+            return
+
         key = f"{metadata_name}_{sequence}"
         key_value = f"{metadata_name}_{sequence}_value"
         match condition: