docs: public void setSubtitle(final String subtitle) {
          if (subtitle == null && this.subtitle == null) {
              return;
          } else if (subtitle == null) {
              removeChild(this.subtitle);
              this.subtitle = null;
          } else if (this.subtitle == null) {
              this.subtitle = new KeyValueNode<String>(CommonConstants.CS_SUBTITLE_TITLE, subtitle);
              appendChild(this.subtitle, false);
          } else {
              this.subtitle.setValue(subtitle);
          }
      }