[1.6.x] Fixed #21568 -- Added missing ModelMultipleChoiceField to_python method

Thanks dibrovsd at gmail.com for the report and Simon Charette
for the review.
Backport of 8a9c8bb90 from master.

1 files changed, 6 insertions, 0 deletions

diff --git a/django/forms/models.py b/django/forms/models.py
index 5c4fe4bbdf..15c0015b89 100644
--- a/django/forms/models.py
+++ b/django/forms/models.py
@@ -1167,6 +1167,12 @@ class ModelMultipleChoiceField(ModelChoiceField):
             msg = _('Hold down "Control", or "Command" on a Mac, to select more than one.')
             self.help_text = string_concat(self.help_text, ' ', msg)
 
+    def to_python(self, value):
+        if not value:
+            return []
+        to_py = super(ModelMultipleChoiceField, self).to_python
+        return [to_py(val) for val in value]
+
     def clean(self, value):
         if self.required and not value:
             raise ValidationError(self.error_messages['required'], code='required')