Cheers! It worked flawlessly this morning. Thanks for tracking that down.
I've tried a number of times to build and run the example mod and keep encountering the same error. I've tried switching JVMs, redownloading the Forge MDK, and restarting my laptop. I followed the steps to start modding available here, starting at 'From Zero to Modding' and, after step #5, jumping to step #2 in 'Building and Testing Your Mod'. Any help is greatly appreciated. Apologies in advance if it's something stupid on my part.