public DomainWildcardMappingBuilder<V> add(String hostname, V output) {
        map.put(normalizeHostName(hostname),
                checkNotNull(output, "output"));
        return this;
    }
@Test
    public void testNullDomainNamePatternsAreForbidden() {
        assertThrows(NullPointerException.class, new Executable() {
            @Override
            public void execute() {
                new DomainWildcardMappingBuilder<String>("NotFound").add(null, "Some value");
            }
        });
    }