@Nullable
    @Contract(value = "null -> null; !null -> !null", pure = true)
    public static Runnable unwrap(@Nullable Runnable runnable) {
        if (!(runnable instanceof TtlRunnable)) return runnable;
        else return ((TtlRunnable) runnable).getRunnable();
    }
Unwrap {@link TtlRunnable} to the original/underneath one.
<p>
this method is {@code null}-safe, when input {@code Runnable} parameter is {@code null}, return {@code null};
if input {@code Runnable} parameter is not a {@link TtlRunnable} just return input {@code Runnable}.
<p>
so {@code TtlRunnable.unwrap(TtlRunnable.get(runnable))} will always return the same input {@code runnable} object.

@see #get(Runnable)
@see com.alibaba.ttl.TtlUnwrap#unwrap(Object)
@since 2.10.2
ttl2-compatible/src/main/java/com/alibaba/ttl/TtlRunnable.java