@NonNullByDefault does not work for type arguments of a local type

[stephan-herrmann]

This program:

		import java.util.Iterator;
		import org.eclipse.jdt.annotation.NonNullByDefault;

		@NonNullByDefault
		public class X {
			Iterator<String> getProcessIterator() {
				abstract class StringIterator implements Iterator<String> { }
				return new StringIterator() {
					@Override
					public boolean hasNext() {
						return false;
					}
					@Override
					public String next() {
						return null;
					}
				};
			}
		}

gets a bogus error report against the return statement:

Null type safety (type annotations): The expression of type '@NonNull ' needs unchecked conversion to conform to '@NonNull Iterator<@NonNull String>', corresponding supertype is 'Iterator<String>'

The error should at least print some type name after @NonNull.

The problem actually lies with the local type, not the anonymous subclass. implements Iterator<String> should be expanded to implements Iterator<@NonNull String> (due to outer @NNBD) but isn't.