code: public Comment addComment(long sheetId, long discussionId, Comment comment) throws SmartsheetException{
          return this.createResource("sheets/" + sheetId + "/discussions/" + discussionId + "/comments", Comment.class, comment);
      }
docs: Add a comment to a discussion.
  
  It mirrors to the following Smartsheet REST API method: POST /discussion/{discussionId}/comments</p>
  
  @param sheetId the sheet id
  @param discussionId the discussion id
  @param comment the comment to add
  @return the created comment
  @throws IllegalArgumentException if any argument is null or empty string
  @throws InvalidRequestException if there is any problem with the REST API request
  @throws AuthorizationException if there is any problem with  the REST API authorization (access token)
  @throws ResourceNotFoundException if the resource cannot be found
  @throws ServiceUnavailableException if the REST API service is not available (possibly due to rate limiting)
  @throws SmartsheetException if there is any other error during the operation