"null" not allowed in package name

Question

I want to create a java package name where one of the elements is the word "null".

Java tells me this is not a valid package:

package org.null.thing;

public class Foo { 
  public static int addThing(int a, int b) { 
    return a + b;
  }
}

The error I get is:

error: <identifier> expected
package org.null.thing;
            ^

Where is this defined? What is the reason for this?

Answer 1

The problem is that null is simply not allowed as "identifier":

An identifier is an unlimited-length sequence of Java letters and Java digits, the first of which must be a Java letter. An identifier cannot have the same spelling (Unicode character sequence) as a keyword (§3.9), boolean literal (§3.10.3), or the null literal (§3.10.7).

Thus org.null.thing is as invalid as or.int.string or other interesting ideas.