fix: 修复表结构预览

src/module/datasource/component/DataTableStruct.jsx

@@ -21,7 +21,7 @@ export default function DataTableStruct({ currentStep, tableData, datax, onRef }
 
   useImperativeHandle(onRef, () => {
     return {
-      jsonValue: jsonValue.current.jsonValue,
+      jsonValue: jsonValue.current ? jsonValue.current.jsonValue : {},
     }
   })