Fix: Nan issue. (#6242)

### What problem does this PR solve?

#6065

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

agent/canvas.py

                 pid = cpn["parent_id"]
                 _, o = cpn["obj"].output(allow_partial=False)
                 _, oo = self.components[pid]["obj"].output(allow_partial=False)
-                self.components[pid]["obj"].set_output(pd.concat([oo.dropna(axis=1), o.dropna(axis=1)], ignore_index=True))
+                self.components[pid]["obj"].set_output(pd.concat([oo.dropna(axis=1), o.dropna(axis=1)], ignore_index=True).dropna())
                 downstream = [pid]
 
             for m in prepare2run(downstream):

agent/component/retrieval.py

                                         rank_feature=label_question(query, kbs))
         else:
             kbinfos = {"chunks": [], "doc_aggs": []}
-            
+
         if self._param.use_kg and kbs:
             ck = settings.kg_retrievaler.retrieval(query,
                                                    [kbs[0].tenant_id],