Prevent creating custom kaehmy role with existing name

webapp/forms.py

@@ -38,7 +38,15 @@ class KaehmyForm_Form(forms.ModelForm):
         if number.isdigit():
             return number
         else:
-            raise ValidationError(_('Invalid value'))
+            raise ValidationError(_('Invalid phone number'))
+
+    def clean_custom_role_name(self):
+        """Check that no other custom role with same name exists."""
+        custom_name = self.cleaned_data.get('custom_role_name')
+        if CustomKaehmyRole.objects.get(name=custom_name) is None:
+            return custom_name
+        else:
+            raise ValidationError(_('Custom role with the same name already exists.'))
 
 
 class KaehmyCommentForm(forms.ModelForm):