When something goes wrong while trying to get the URL for pageClass/pageParameters using RequestCycle, the exception message and its stacktrace is not very helpful in tracking down the component actually causing the problem. (See attached stacktrace that I while rendering a BookmarkablePageLink with a null parameter.)
I suggest to catch any exceptions thrown by urlFor(IRequestHandler) and throwing a WicketRuntimeException having pageClass and pageparamters in its message. (See attached patch)