fix: fix node valid detect (#21709)

web/app/components/workflow/nodes/_base/components/variable/var-reference-picker.tsx

@@ -184,10 +184,12 @@ const VarReferencePicker: FC<Props> = ({
       return startNode?.data
 
     const node = getNodeInfoById(availableNodes, outputVarNodeId)?.data
+    if (node) {
       return {
         ...node,
         id: outputVarNodeId,
       }
+    }
   }, [value, hasValue, isConstant, isIterationVar, iterationNode, availableNodes, outputVarNodeId, startNode, isLoopVar, loopNode])
 
   const isShowAPart = (value as ValueSelector).length > 2