org.codehaus.groovy.runtime.MetaClassHelper#getClassWithNullAndWrapper should return NullObject when accept null

I have a extension class

class NumberExtension {
    static Integer plus(Integer self, NullObject right) {
        return self;
    }
}

However

1 + null

will throw

Ambiguous method overloading for method java.lang.Integer#plus

Because org.codehaus.groovy.runtime.MetaClassHelper#getClassWithNullAndWrapper return null for null argument. Then org.codehaus.groovy.runtime.MetaClassHelper#calculateParameterDistance(java.lang.Class, org.codehaus.groovy.reflection.CachedClass) doesn't return 0 because null != NullObject.class