fix: undefined match the wrong output schema (#25971)

web/app/components/workflow/nodes/_base/components/variable/use-match-schema-type.ts

 import matchTheSchemaType from './match-schema-type'
 
 export const getMatchedSchemaType = (obj: AnyObj, schemaTypeDefinitions?: SchemaTypeDefinition[]): string => {
-  if(!schemaTypeDefinitions) return ''
+  if(!schemaTypeDefinitions || obj === undefined || obj === null) return ''
   const matched = schemaTypeDefinitions.find(def => matchTheSchemaType(obj, def.schema))
   return matched ? matched.name : ''
 }