Help with guest error when no fourth party member

[Mestino]

Okay, I have a guest instead of having a fourth party member and I got the image there and everything, but when there isn't a guest an error comes up. I was wondering if anyone knew how to fix this. This error comes up.
Script 'Window_Base' line 109: NoMethodError occurred
undefined method 'character_name' for nil:NilClass

I don't know how to get it to work, but I think I need to use a if and else in order to fix my problem.

 

[Mestino]

Never mind. I found a way to fix it, but I thank anyone who had attempted to help.