Cmon, man, give us a CLUE. like the relevant part of the log with the exception.
Usually npe here means wrong config., usually wrong url. Also some dbs, maybe including mysql, need you to supply a username even if they don't use it for anything. Don't know about password.
Sorry about omitting the log entry...
I did get it working, and I'll pass along a tip for those (myself included) who should know better... When using the mm.mysql driver, make sure that the url is in the form "jdbc:mysql://servername/db" instead of "jdbc:mysql//servername/db" (remember the colon after mysql). It saves head-banging.