javacc java.lang.NullPointerException

Question

im trying to make a miniJava parser but im having trouble figuring out a way to parse method declarations that have no formal parameters. e.g public int getNumber() The code that i have right now works for parameters of one or more, but im not sure how to return an empty formal object as clearly the problem lies with the line returning null. Is there a way to skip the return statement altogether and return nothing?

public Formal nt_FormalList() :
{
    Type t;
    Token s;
    LinkedList<Formal> fl = new LinkedList<Formal>();
    Formal f;

}
{
    t = nt_Type() s = <IDENTIFIER> (f = nt_FormalRest() {fl.add(f);})*
    { return new Formal(t, s.image); }

    | {}    
    { return null; }
}

.....

public class Formal {

    public final Type t;
    public final String i;

    public Formal(Type at, String ai) {
        t = at;
        i = ai;
    }

Answer 1

I'd suggest that you return list of Formals from nt_FormalList.

public List<Formal> nt_FormalList() :
{
    LinkedList<Formal> fl = new LinkedList<Formal>();
    Formal f;
}
{
    [ f = nt_Formal() {fl.add(f);}
      (<COMMA> f = nt_Formal() {fl.add(f);})*
    ]
    { return fl; }
}