code: @Override
      public final <B> Maybe<B> fmap(Function<? super A, ? extends B> fn) {
          return Monad.super.<B>fmap(fn).coerce();
      }
docs: {@inheritDoc}
  <p>
  If the value is present, return {@link Maybe#just} <code>fn</code> applied to the value; otherwise, return
  {@link Maybe#nothing}.