fixed score threshold is none (#8342)

api/core/rag/retrieval/dataset_retrieval.py

                         top_k=top_k,
                         score_threshold=retrieval_model.get("score_threshold", 0.0)
                         if retrieval_model["score_threshold_enabled"]
-                        else None,
+                        else 0.0,
                         reranking_model=retrieval_model.get("reranking_model", None)
                         if retrieval_model["reranking_enable"]
                         else None,

api/core/tools/tool/dataset_retriever/dataset_multi_retriever_tool.py

                         top_k=self.top_k,
                         score_threshold=retrieval_model.get("score_threshold", 0.0)
                         if retrieval_model["score_threshold_enabled"]
-                        else None,
+                        else 0.0,
                         reranking_model=retrieval_model.get("reranking_model", None)
                         if retrieval_model["reranking_enable"]
                         else None,

api/core/tools/tool/dataset_retriever/dataset_retriever_tool.py

                     top_k=self.top_k,
                     score_threshold=retrieval_model.get("score_threshold", 0.0)
                     if retrieval_model["score_threshold_enabled"]
-                    else None,
+                    else 0.0,
                     reranking_model=retrieval_model.get("reranking_model", None)
                     if retrieval_model["reranking_enable"]
                     else None,

api/services/hit_testing_service.py

             top_k=retrieval_model.get("top_k", 2),
             score_threshold=retrieval_model.get("score_threshold", 0.0)
             if retrieval_model["score_threshold_enabled"]
-            else None,
+            else 0.0,
             reranking_model=retrieval_model.get("reranking_model", None)
             if retrieval_model["reranking_enable"]
             else None,