Odoo Server Error

Traceback (most recent call last):
  File "/opt/openerp/odoo/openerp/http.py", line 544, in _handle_exception
    return super(JsonRequest, self)._handle_exception(exception)
  File "/opt/openerp/odoo/openerp/http.py", line 581, in dispatch
    result = self._call_function(**self.params)
  File "/opt/openerp/odoo/openerp/http.py", line 317, in _call_function
    return checked_call(self.db, *args, **kwargs)
  File "/opt/openerp/odoo/openerp/service/model.py", line 118, in wrapper
    return f(dbname, *args, **kwargs)
  File "/opt/openerp/odoo/openerp/http.py", line 314, in checked_call
    return self.endpoint(*a, **kw)
  File "/opt/openerp/odoo/openerp/http.py", line 810, in __call__
    return self.method(*args, **kw)
  File "/opt/openerp/odoo/openerp/http.py", line 410, in response_wrap
    response = f(*args, **kw)
  File "/opt/openerp/odoo/addons/web/controllers/main.py", line 948, in call_button
    action = self._call_kw(model, method, args, {})
  File "/opt/openerp/odoo/addons/web/controllers/main.py", line 936, in _call_kw
    return getattr(request.registry.get(model), method)(request.cr, request.uid, *args, **kwargs)
  File "/opt/openerp/odoo/openerp/api.py", line 268, in wrapper
    return old_api(self, *args, **kwargs)
  File "/opt/openerp/odoo/openerp/addons/sun_helpdesk /wizard/assign_case.py", line 22, in assign_case
    record_id = context.get('active_id')
AttributeError: 'NoneType' object has no attribute 'get'