GHOST368'S PROFILE

Hi I'm very new to rpgmaker and I think I fucked something up.

I've been play testing my game as I go and today I noticed that every time I try to look at the status menu, I get an error message that says:

Script 'Window_Base'line 310:NoMethodError occurred.
undefined method 'upcase' for nil:NilClass
(Sorry I would include an image but it only allows images with links)

I thought that it happened because I added a self made class but when I tested that method in another game, that worked fine. I also tried copy pasting the entire Window_Base script from a fresh game to this and still nothing.
If anyone has any idea what this could be or what to do I would really, really appreciate it! This is in RPGMaker VX Ace btw