Merge pull request #1827 from aitormagan/1710-empty_non_existing_fields

Replace missing_fields by non_existing_filed_names in order to get correctly the list of non existing fields.

Fix #1710.

ckanext/datastore/db.py

@@ -644,7 +644,7 @@ def upsert_data(context, data_dict):
             if non_existing_filed_names:
                 raise ValidationError({
                     'fields': [u'fields "{0}" do not exist'.format(
-                        ', '.join(missing_fields))]
+                        ', '.join(non_existing_filed_names))]
                 })
 
             unique_values = [record[key] for key in unique_keys]