Debugging Code Assistant

Based on your provided code snippet and problem description, the NullPointerException is occurring because you're trying to call a method on a null object. In your code, str is a static String that isn't initialized, hence it defaults to null. When you try to call toString() on str, a NullPointerException is thrown.
Here's how you can resolve the issue:
public class Test {
    private static String str = "";
    public static void main(String[] args) {
        System.out.println(str.toString());
    }
}

In this revised version, str is initialized to an empty string "". This prevents the NullPointerException as str is no longer null. 
If you're still facing issues after initializing str, the problem could be elsewhere in your code. Make sure all objects are properly initialized before you attempt to call methods on them. Always remember, a NullPointerException means that an object was not initialized (i.e., it is null) and a method or attribute was invoked on that object.