@Nullable
    public <R> R custom(@NotNull Function<Exceptional<T>, R> function) {
        Objects.requireNonNull(function);
        return function.apply(this);
    }
@ Nullable public < R > R custom ( @ NotNull Function < Exceptional < T > , R > function ) { Objects . requireNonNull ( function ) ; return function . apply ( this ) ; }
Applies custom operator on {@code Exceptional}.

@param <R> the type of the result
@param function  a transforming function
@return a result of the transforming function
@throws NullPointerException if {@code function} is null
@since 1.1.9