public final Optional<Button> getButton(ButtonType buttonType) {
    if (Objects.isNull(getDialogControl())) {
      return Optional.empty();
    } else {
      return getDialogControl().getButton(buttonType);
    }
  }
Retrieves the {@link Button} instance of the {@link DialogControl} which is of the
specified {@link ButtonType}.

@param buttonType to retrieve from the {@link DialogControl}
@return the button or an empty {@link Optional}, if the {@link DialogControl} hasn't been
        initialized before
workbenchfx-core/src/main/java/com/dlsc/workbenchfx/model/WorkbenchDialog.java