api: replace unicode by force_text (#28962)

src/authentic2/api_views.py

@@ -21,6 +21,7 @@ from django.db import models
 from django.contrib.auth import get_user_model
 from django.core.exceptions import MultipleObjectsReturned
 from django.utils.translation import ugettext as _
+from django.utils.encoding import force_text
 from django.views.decorators.vary import vary_on_headers
 from django.views.decorators.cache import cache_control
 from django.shortcuts import get_object_or_404
@@ -221,7 +222,7 @@ class Register(BaseRpcView):
                     'errors': {
                         '__all__': ['Mail sending failed']
                     },
-                    'exception': unicode(e),
+                    'exception': force_text(e),
                 }
                 response_status = status.HTTP_503_SERVICE_UNAVAILABLE
             else: