code: @CheckReturnValue
      public MessageAction content(final String content)
      {
          if (content == null || content.isEmpty())
              this.content.setLength(0);
          else if (content.length() <= Message.MAX_CONTENT_LENGTH)
              this.content.replace(0, this.content.length(), content);
          else
              throw new IllegalArgumentException(CONTENT_TOO_BIG);
          return this;
      }
docs: Overrides existing content with the provided input
  <br>The content of a Message may not exceed {@value Message#MAX_CONTENT_LENGTH}!
  
  @param  content
  Sets the specified content and overrides previous content
  or {@code null} to reset content
  
  @throws java.lang.IllegalArgumentException
  If the provided content exceeds the {@value Message#MAX_CONTENT_LENGTH} character limit
  
  @return Updated MessageAction for chaining convenience