Schema-transformer is nonetype and want to acess instance's attributes

I'm not able to reproduce the situation for now.

But I get the following traceback regarding the schema-transformer service:

Traceback (most recent call last):
  File "/usr/bin/contrail-schema", line 11, in <module>
    load_entry_point('schema-transformer==0.1.dev0', 'console_scripts', 'contrail-schema')()
  File "/usr/lib/python2.7/dist-packages/schema_transformer/to_bgp.py", line 708, in server_main
    main()
  File "/usr/lib/python2.7/dist-packages/schema_transformer/to_bgp.py", line 702, in main
    st_logger, args)
  File "/usr/lib/python2.7/dist-packages/cfgm_common/zkclient.py", line 346, in master_election
    self._election.run(func, *args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/kazoo/recipe/election.py", line 53, in run
    func(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/schema_transformer/to_bgp.py", line 646, in run_schema_transformer
    transformer = SchemaTransformer(st_logger, args)
  File "/usr/lib/python2.7/dist-packages/schema_transformer/to_bgp.py", line 180, in __init__
    SchemaTransformer.destroy_instance()
  File "/usr/lib/python2.7/dist-packages/schema_transformer/to_bgp.py", line 384, in destroy_instance
    inst._vnc_amqp.close()
AttributeError: 'NoneType' object has no attribute '_vnc_amqp'