code: public Expression expression(Member author, String content, Expression inReplyTo) {
          Expression expression = new Expression(instance);
          expression.setAuthor(author);
          expression.setContent(content);
          expression.setInReplyTo(inReplyTo);
          expression.save();
          return expression;
      }
docs: Adds new Expression in Reply To an existing Expression.
  @param author Author of Expression.
  @param content Content of Expression.
  @param inReplyTo Expression being replied to.
  @return Newly created Conversation