Abort on null-returning implied toString (was System.out.println....precedence)

[Mark J Roberts <mjr at anarcast dot net>]

Tom Tromey:
> "The Java Programming Language" (not canonical, but maybe useful) does
> have a table of operator precedence; it shows binary `+' having
> precedence over `?:'.

Oops. Sorry.

That said, with today's trunk, an implied toString which returns null will
cause an abort w/ core dump:

public class Test {
    public static void main(String args[]) {
        System.out.println(new Test());
    }
    public String toString() { return null; }
}

$ ./test
Aborted (core dumped)

When the toString is explicit it works as I expect:

    System.out.println((new Test()).toString());

$ ./test
null

as does println((String)null).