Explicit check for None to fix ubo system error

bluesky/ui/qtgl/glhelpers.py

@@ -329,7 +329,7 @@ def select(self):
     def update_ubo(self, uboname, *args, **kwargs):
         ''' Update an uniform buffer object of this shader set. '''
         ubo = self._ubos.get(uboname, None)
-        if not ubo:
+        if ubo is None:
             raise KeyError('Uniform Buffer Object', uboname,
                            'not found in shader set.')
         ubo.update(*args, **kwargs)