BUG: Use less ambiguous conditional check

Author: bnmajor

itkwidgets/viewer.py

@@ -70,7 +70,7 @@ async def run(self, ctx):
                 result = await _get_viewer_image(data)
             elif render_type is RenderType.POINT_SET:
                 result = await _get_viewer_point_sets(data)
-            if not result:
+            if result is None:
                 result = data
             self.init_data[key] = result