I can't get your code to run at all, but I see at least two problems that you need to fix before you'll get anywhere. First, name your class something besides Null. That's a reserved word. Second, look carefully at line 28 and you'll find something wrong.
Java is case-sensitive, true. But the underlying OS may not be, and that has resulted in problems on more than one occasion.
Actually, I had a package named "com.mycompany.financials.servapp.core.floomod" or something like that and ran into issues because "core" is the default name for a core dump file and at the time in question, the OS mis-interpreted the "core" directory name to think it was working with a core dump.
So you cannot just just any old name with impunity.
Besides, while the compiler knows that "Null", "NULL" and "null" are different things, when you discuss them with colleages, the relative capitalizations are not going to be as apparent, which can result in a whole lot of confusion.