code: public final static <T> Stream<T> optionalToStream(final Optional<T> optional) {
          if (optional.isPresent())
              return Stream.of(optional.get());
          return Stream.of();
      }
docs: Convert an Optional to a Stream
  
  <pre>
  {@code
  Stream<Integer> stream = Streams.optionalToStream(Optional.of(1));
  //Stream[1]
  
  Stream<Integer> zero = Streams.optionalToStream(Optional.zero());
  //Stream[]
  }
  </pre>
  
  @param optional Optional to convert to a Stream
  @return Stream with a single value (if present) created from an Optional