Refs #26709 -- Added type check for models.Index fields argument.

django/db/models/indexes.py

@@ -14,6 +14,8 @@ class Index(object):
     suffix = 'idx'
 
     def __init__(self, fields=[], name=None):
+        if not isinstance(fields, list):
+            raise ValueError('Index.fields must be a list.')
         if not fields:
             raise ValueError('At least one field is required to define an index.')
         self.fields = fields

tests/model_indexes/tests.py

@@ -22,6 +22,10 @@ class IndexesTests(TestCase):
         self.assertEqual(index, same_index)
         self.assertNotEqual(index, another_index)
 
+    def test_index_fields_type(self):
+        with self.assertRaisesMessage(ValueError, 'Index.fields must be a list.'):
+            models.Index(fields='title')
+
     def test_raises_error_without_field(self):
         msg = 'At least one field is required to define an index.'
         with self.assertRaisesMessage(ValueError, msg):