Traceback in response when try to get list of services for nonexistent environment

Steps to reproduce:
1. Install murano from 0.4 branch
2. Send GET request to http://<murano-url>:8082/environments/None/services, with correct parameter in headers : "X-Configuration-Session: <valid-session-id>"

Actual result:
We get the following traceback:
2014-01-16 10:25:41.395 7087 DEBUG muranoapi.api.v1.services [-] Services:Get <EnvId: None, Path: /services> get /usr/local/lib/python2.7/dist-packages/muranoapi/api/v1/services.py:44
2014-01-16 10:25:41.412 7087 INFO eventlet.wsgi [-] Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/eventlet/wsgi.py", line 384, in handle_one_response
    result = self.application(self.environ, start_response)
  File "/usr/lib/python2.7/dist-packages/keystoneclient/middleware/auth_token.py", line 539, in __call__
    return self.app(env, start_response)
  File "/usr/local/lib/python2.7/dist-packages/webob/dec.py", line 130, in __call__
    resp = self.call_func(req, *args, **self.kwargs)
  File "/usr/local/lib/python2.7/dist-packages/webob/dec.py", line 195, in call_func
    return self.func(req, *args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/muranoapi/openstack/common/wsgi.py", line 194, in __call__
    response = req.get_response(self.application)
  File "/usr/local/lib/python2.7/dist-packages/webob/request.py", line 1296, in send
    application, catch_exc_info=False)
  File "/usr/local/lib/python2.7/dist-packages/webob/request.py", line 1260, in call_application
    app_iter = application(self.environ, start_response)
  File "/usr/local/lib/python2.7/dist-packages/webob/dec.py", line 144, in __call__
    return resp(environ, start_response)
  File "/usr/local/lib/python2.7/dist-packages/routes/middleware.py", line 131, in __call__
    response = self.app(environ, start_response)
  File "/usr/local/lib/python2.7/dist-packages/webob/dec.py", line 144, in __call__
    return resp(environ, start_response)
  File "/usr/local/lib/python2.7/dist-packages/webob/dec.py", line 130, in __call__
    resp = self.call_func(req, *args, **self.kwargs)
  File "/usr/local/lib/python2.7/dist-packages/webob/dec.py", line 195, in call_func
    return self.func(req, *args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/muranoapi/openstack/common/wsgi.py", line 378, in __call__
    action_result = self.execute_action(action, request, **action_args)
  File "/usr/local/lib/python2.7/dist-packages/muranoapi/openstack/common/wsgi.py", line 392, in execute_action
    return self.dispatch(self.controller, action, request, **action_args)
  File "/usr/local/lib/python2.7/dist-packages/muranoapi/openstack/common/wsgi.py", line 401, in dispatch
    return method(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/muranoapi/api/v1/services.py", line 35, in f_normalize_path
    return f(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/muranoapi/api/v1/services.py", line 51, in get
    result = CoreServices.get_data(environment_id, path, session_id)
  File "/usr/local/lib/python2.7/dist-packages/muranoapi/db/services/core_services.py", line 57, in get_data
    srv['status'] = get_status(environment_id, srv['id'])
  File "/usr/local/lib/python2.7/dist-packages/muranoapi/db/services/core_services.py", line 41, in get_service_status
    return EnvironmentServices.get_status(environment_id)
  File "/usr/local/lib/python2.7/dist-packages/muranoapi/db/services/environments.py", line 66, in get_status
    SessionState.deploying)
  File "/usr/local/lib/python2.7/dist-packages/muranoapi/db/services/sessions.py", line 52, in get_sessions
    Session.version == environment.version
AttributeError: 'NoneType' object has no attribute 'version'