@Nullable
    public static <T> Handler<T> unwrap(@Nullable Handler<T> handler) {
        if (!(handler instanceof TtlVertxHandler)) {
            return handler;
        } else {
            return ((TtlVertxHandler<T>) handler).getHandler();
        }
    }
Unwrap {@link TtlVertxHandler} to the original/underneath one.
<p>
this method is {@code null}-safe, when input {@code Function} parameter is {@code null}, return {@code null};
if input {@code Function} parameter is not a {@link TtlVertxHandler} just return input {@code Function}.
<p>
so {@code TtlVertxHandler.unwrap(TtlVertxHandler.get(function))} will always return the same input {@code function} object.

@see #handle(Object)
@see com.alibaba.ttl.TtlUnwrap#unwrap(Object)
ttl-integrations/vertx3-ttl-integration/src/main/java/com/alibaba/ttl/integration/vertx3/TtlVertxHandler.java