Only extract validation error messages from ValidationError exception instances.

mayan/apps/metadata/views.py

@@ -2,7 +2,7 @@ from __future__ import absolute_import, unicode_literals
 
 from django.conf import settings
 from django.contrib import messages
-from django.core.exceptions import PermissionDenied
+from django.core.exceptions import PermissionDenied, ValidationError
 from django.core.urlresolvers import reverse, reverse_lazy
 from django.http import HttpResponseRedirect
 from django.shortcuts import get_object_or_404, render_to_response
@@ -127,18 +127,22 @@ def metadata_edit(request, document_id=None, document_id_list=None):
                         except Exception as exception:
                             errors.append(exception)
 
-                if errors:
                 for error in errors:
                     if settings.DEBUG:
                         raise
                     else:
+                        if isinstance(error, ValidationError):
+                            exception_message = ', '.join(error.messages)
+                        else:
+                            exception_message = unicode(error)
+
                         messages.error(
                             request, _(
                                 'Error editing metadata for document: '
                                 '%(document)s; %(exception)s.'
                             ) % {
                                 'document': document,
-                                    'exception': ', '.join(exception.messages)
+                                'exception': exception_message
                             }
                         )
                 else: