@NonNull
    public static <T> List<Callable<T>> unwraps(@Nullable Collection<? extends Callable<T>> tasks) {
        if (tasks == null) return Collections.emptyList();

        List<Callable<T>> copy = new ArrayList<>();
        for (Callable<T> task : tasks) {
            if (!(task instanceof TtlCallable)) copy.add(task);
            else copy.add(((TtlCallable<T>) task).getCallable());
        }
        return copy;
    }
Unwrap {@link TtlCallable} to the original/underneath one.
<p>
Invoke {@link #unwrap(Callable)} for each element in input collection.
<p>
This method is {@code null}-safe, when input {@code Callable} collection parameter is {@code null}, return an empty list.

@see #gets(Collection)
@see #unwrap(Callable)
ttl-core/src/main/java/com/alibaba/ttl3/TtlCallable.java