Refactor column validation in File class to emit parse error event when columns are invalid

src/models/file.js

@@ -124,8 +124,9 @@ class File {
     const stream = new PassThrough();
 
     // check if columns is valid
-    if (!columns || columns.length) {
+    if (!columns || !columns.length) {
       // return Promise.reject(new Error('Invalid columns'));
+      emitter.emit('parse.error', { url: this.url, filepath: this.filepath, error: 'Invalid columns' });
       return false;
     }