error while returning json in webserver function

[9exbizy]

Hello All,

I have been trying to run my function to return json using return json.dumps(mybuilder.container.to_provJSON())

but I keep getting the error below when I run in debug mode,

are there any ideas on why I will be getting this error?

Traceback (most recent call last):

  File "c:\python26\lib\site-packages\web.py-0.36-py2.6.egg\web\application.py", line 237, in process

    return self.handle()

  File "c:\python26\lib\site-packages\web.py-0.36-py2.6.egg\web\application.py", line 228, in handle

    return self._delegate(fn, self.fvars, args)

  File "c:\python26\lib\site-packages\web.py-0.36-py2.6.egg\web\application.py", line 409, in _delegate

    return handle_class(cls)

  File "c:\python26\lib\site-packages\web.py-0.36-py2.6.egg\web\application.py", line 385, in handle_class

    return tocall(*args)

  File "C:\Users\9exbizy\workspace_indigo\Project\src\Webserver.py", line 454, in GET

    return json.dumps(mybuilder.container.to_provJSON())

  File "C:\Python26\Lib\site-packages\pyprov\model\bundle.py", line 352, in to_provJSON

    Bundle.to_provJSON(self,nsdict)

  File "C:\Python26\Lib\site-packages\pyprov\model\bundle.py", line 74, in to_provJSON

    jsondict = relation.to_provJSON(nsdict)

  File "C:\Python26\Lib\site-packages\pyprov\model\relation.py", line 594, in to_provJSON

    self._json[self._idJSON]['prov:subordinate']=self.subordinate._idJSON

AttributeError: 'NoneType' object has no attribute '_idJSON'