code: public static <A> Maybe<A> maybe(A a) {
          return a == null ? nothing() : just(a);
      }
docs: Lift a potentially null value into {@link Maybe}. If <code>a</code> is not null, returns <code>just(a)</code>;
  otherwise, returns {@link #nothing()}.
  
  @param a   the potentially null value
  @param <A> the value parameter type
  @return "Just" the value, or nothing