That error message is part of a "gack". Gacks are salesforce internal errors that you can't usually fix on your own. Think of them as an unhandled salesforce error.
Theres a lot of resources out there about gacks but at the end of the day they all say the same thing - only salesforce knows what this error means and only salesforce can fix it.
What is a Gack?
What you are looking at is what we call a GACK. A gack is our blue screen of death, our frowny Mac icon, our “the number you have reached is no longer in service”, our “Jedediah has died of dysentery”. A gack is what happens when an error got thrown within our application and we didn’t catch it and handle it.
What this means is that it’s not your fault. It’s ours. That’s why we apologize in that message. Sorry!
This friendly message is the above-water portion of a huge iceberg of functionality. The numbers you see are part of an elaborate system for efficiently bringing these events to the attention of R&D. This post will help you understand that system, and how you can help us in getting you running safely. (Hint: steer away from icebergs.)
This blog post goes into detail about some aspects of the gack and how to report it. It offers great advice, expect for posting on stack exchange - we really can't help you fix this exception. Sometimes, maybe, if its caused by code you wrote but not something baked into the standard functionality of salesforce.