add missing haystack import

panikweb/search.py

@@ -2,6 +2,7 @@ import haystack.backends.solr_backend
 from haystack.query import SearchQuerySet
 from haystack.constants import ID, DJANGO_CT, DJANGO_ID
 from haystack.utils import get_identifier
+from haystack.backends import EmptyResults
 
 from pysolr import SolrError