[BUG] When we create a new project manually appear a traceback.

Hello all/

When you install this module, a traceback appear when you create manually a project.

OpenERP Server Error
Client Traceback (most recent call last):
  File "/home/production/openerp7_production/web/addons/web/http.py", line 203, in dispatch
    response["result"] = method(self, **self.params)
  File "/home/production/openerp7_production/web/addons/web/controllers/main.py", line 1129, in call_kw
    return self._call_kw(req, model, method, args, kwargs)
  File "/home/production/openerp7_production/web/addons/web/controllers/main.py", line 1121, in _call_kw
    return getattr(req.session.model(model), method)(*args, **kwargs)
  File "/home/production/openerp7_production/web/addons/web/session.py", line 43, in proxy
    result = self.proxy.execute_kw(self.session._db, self.session._uid, self.session._password, self.model, method, args, kw)
  File "/home/production/openerp7_production/web/addons/web/session.py", line 31, in proxy_method
    result = self.session.send(self.service_name, method, *args)
  File "/home/production/openerp7_production/web/addons/web/session.py", line 104, in send
    raise xmlrpclib.Fault(openerp.tools.ustr(e), formatted_info)

Server Traceback (most recent call last):
  File "/home/production/openerp7_production/web/addons/web/session.py", line 90, in send
    return openerp.netsvc.dispatch_rpc(service_name, method, args)
  File "/home/production/openerp7_production/server/openerp/netsvc.py", line 293, in dispatch_rpc
    result = ExportService.getService(service_name).dispatch(method, params)
  File "/home/production/openerp7_production/server/openerp/service/web_services.py", line 626, in dispatch
    res = fn(db, uid, *params)
  File "/home/production/openerp7_production/server/openerp/osv/osv.py", line 188, in execute_kw
    return self.execute(db, uid, obj, method, *args, **kw or {})
  File "/home/production/openerp7_production/server/openerp/osv/osv.py", line 131, in wrapper
    return f(self, dbname, *args, **kwargs)
  File "/home/production/openerp7_production/server/openerp/osv/osv.py", line 197, in execute
    res = self.execute_cr(cr, uid, obj, method, *args, **kw)
  File "/home/production/openerp7_production/server/openerp/osv/osv.py", line 185, in execute_cr
    return getattr(object, method)(cr, uid, *args, **kw)
  File "/home/production/openerp7_production/com_addons/project_wbs/project_wbs.py", line 88, in create
    parent_wbs = self.browse(cr, uid, parent_id)[0].wbs
  File "/home/production/openerp7_production/server/openerp/osv/orm.py", line 383, in __getitem__
    raise KeyError(error_msg)
KeyError: "Field '0' does not exist in object 'browse_record(project.project, 0)'"