Begin working with interceptors - not working
Possible reasons:
-Actions invoked by interceptor may not be recieving parameters.
    (example: how is "userName" and "password" sent to the action via
    the interceptor)
-Result returned from interceptor only looks at global results,
    not results specific to the action login.
-Methods defined to be excluded by the interceptor are not being excluded.
interceptor successfully accepts parameters- needed defaultStack interceptor-ref
null pointer exception thrown before testing if value is null