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Corrected model method return values

ref-test/app/models/dataset.py

@@ -2,7 +2,7 @@ from ..data import data
 from ..modules import db
 from ..tools.logs import write
 
-from flask import flash, jsonify
+from flask import flash
 from flask_login import current_user
 from werkzeug.utils import secure_filename
 
@@ -41,11 +41,11 @@ class Dataset(db.Model):
         if self.default:
             message = 'Cannot delete the default dataset.'
             flash(message, 'error')
-            return False, jsonify({'error': message})
+            return False, message
         if Dataset.query.all().count() == 1:
             message = 'Cannot delete the only dataset.'
             flash(message, 'error')
-            return False, jsonify({'error': message})
+            return False, message
         write('system.log', f'Dataset {self.id} deleted by {current_user.get_username()}.')
         filename = secure_filename('.'.join([self.id,'json']))
         file_path = path.join(data, 'questions', filename)