Static variable evaluates to null at json.put()

Question

I have a class only to store variables as keys like:

public class V {
    public static final String SHOW_OR_FOUND = "show_or_found";
    public static final int FAULT = -1;
}

I use them for keys and comparison, so it's more readable and avoids failures.

Now the problem. If I do something like the following in a method of another class:

JSONObject json = new JSONObject();
json.put(V.SHOW_OR_FOUND, "something important to save")

it won't work. With debugger tool I can see V.SHOW_OR_FOUND evaluates to null. If I do something like:

String test = V.SHOW_OR_FOUND;
json.put(test, "something important to save")

it works. Also, if I use V by calling its own class method, it works perfectly fine.

this.save(V.SHOW_OR_FOUND, "something important to save")

I'm pulling my hairs over this because it makes absolutely no sense to me. Can please someone explain and give a solution to it?

I already tried things like:

String.valueOf(V.SHOW_OR_FOUND)
V.SHOW_OR_FOUND.toString()

The latter results in a NullPointerException, and yes I double and triple checked for spelling faults, even copy pasted the variable name.