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)