java.awt.GraphicsEnvironment.getAvailableFontFamilyNames(Locale l) throws NullPointerException when null is passed as the argument. But as per doc it is supposed to return an array containing all font family names available in the
GraphicsEnvironment when null is passed for the Locale argument.

sample test is below
-------------------
import java.awt.*;

public class Test{

public static void main(String[] args){
GraphicsEnvironment ge = GraphicsEnvironment.
            getLocalGraphicsEnvironment();
        String[] fnts = ge.getAvailableFontFamilyNames(null);
       
}
}