tests: add dataviz null visualization (#48865)

tests/test_dataviz.py

@@ -119,6 +119,12 @@ VISUALIZATION_JSON = [
         'name': 'eleventh visualization (not found)',
         'slug': 'eleventh',
     },
+    {
+        'data-url': 'https://bijoe.example.com/visualization/12/json/',
+        'path': 'https://bijoe.example.com/visualization/12/iframe/?signature=123',
+        'name': 'twelth visualization (all null)',
+        'slug': 'twelth',
+    },
 ]
 
 
@@ -217,6 +223,14 @@ def bijoe_mock(url, request):
             'detail': 'not found',
         }
         return {'content': json.dumps(response), 'request': request, 'status_code': 404}
+    if url.path == '/visualization/12/json/':
+        response = {
+            'format': '1',
+            'data': [None, None],
+            'axis': {'x_labels': ['web', 'mail']},
+            'measure': 'integer',
+        }
+        return {'content': json.dumps(response), 'request': request, 'status_code': 200}
 
 
 @pytest.fixture
@@ -423,6 +437,13 @@ def test_chartng_cell_hide_null_values(app, statistics):
         ([122, 114, 2, 33], {'title': u'bar'}),
     ]
 
+    # all null
+    cell.statistic = Statistic.objects.get(slug='twelth')
+    cell.save()
+    chart = cell.get_chart()
+    assert chart.x_labels == []
+    assert chart.raw_series == [([], {'title': ''})]
+
 
 @with_httmock(bijoe_mock)
 def test_chartng_cell_sort_order_alpha(app, statistics):