diff --git a/bijoe/visualization/views.py b/bijoe/visualization/views.py
index d870062..a69ded8 100644
--- a/bijoe/visualization/views.py
+++ b/bijoe/visualization/views.py
@@ -301,7 +301,7 @@ class VisualizationJSONView(generics.GenericAPIView):
                 }
             elif len(drilldowns) == 1:
                 table = list(visualization.data())
-                axis_data = [x[0]['value'].strip() for x in table]
+                axis_data = [(x[0]['value'] or '').strip() for x in table]
                 data = [x[1]['value'] for x in table]
                 if visualization.drilldown_x:
                     axis = {'x_labels': axis_data}