fixes arteria#65

Author: tehfink

cmsplugin_contact_plus/models.py

@@ -103,7 +103,7 @@ def recaptcha_installed():
 class ExtraField(SortableMixin):
     """
     """
-    form = models.ForeignKey(ContactPlus, verbose_name=_("Contact Form"), on_delete=models.CASCADE)
+    form = models.ForeignKey(ContactPlus, verbose_name=_("Contact Form"), null=True, on_delete=models.SET_NULL)
     label = models.CharField(_('Label'), max_length=100)
     fieldType = models.CharField(max_length=100, choices=FIELD_TYPE)
     initial = models.CharField(