“AWT-EventQueue-0”java.lang.NullPointerException

I'm getting a ''Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException'' in my code. I have no idea why and where this exception occurs. The compilation works fine but sometimes I get this error at runtime. Can I have some help here? The full error message is this:I'm getting a ''Exception in thread "AWT-EventQ