protected validateFileName(name: string, parent: FileStat): string {
     if (!validFilename(name)) {
         return 'Invalid file name, try another.';
     }
     if (parent.children) {
         for (const child of parent.children) {
             if (new URI(child.uri).path.base === name) {
                 return 'A file with this name already exists.';
             }
         }
     }
     return '';
 }
 validate: value => value === '' || validFilename(value),