add null check when use onVersionMismatch method

src/client/js/components/Admin/ImportData/GrowiArchive/UploadForm.jsx

@@ -37,7 +37,7 @@ class UploadForm extends React.Component {
       this.props.onUpload(data);
     }
     catch (err) {
-      if (err[0].code === 'versions-are-not-met') {
+      if (err[0].code === 'versions-are-not-met' && this.props.onVersionMismatch !== null) {
         this.props.onVersionMismatch(err[0].code);
       }
       else {