public Array getArray(String name) {
        Array a = arrayMap.get(name);
        if (a == null) {
            validateArray(name);
            a = new Array(configDefinition, name);
            arrayMap.put(name, a);
        }
        return a;
    }
@Test(expected=IllegalStateException.class)
    public void require_that_append_conflicts_with_index() {
        ConfigPayloadBuilder builder = new ConfigPayloadBuilder();
        ConfigPayloadBuilder.Array array = builder.getArray("foo");
        array.set(0, "bar");
        array.append("baz");
    }