docs: @Nonnull
    public static final AjaxFunctionDeclaration addAjax (@Nullable final String sPrefix,
                                                         @Nonnull final IAjaxExecutor aExecutor)
    {
      // null means random name
      final String sFuncName = StringHelper.hasText (sPrefix) ? sPrefix + AjaxFunctionDeclaration.getUniqueFunctionID ()
                                                              : null;
      final AjaxFunctionDeclaration aFunction = AjaxFunctionDeclaration.builder (sFuncName)
                                                                       .withExecutor (aExecutor)
                                                                       .build ();
      GlobalAjaxInvoker.getInstance ().getRegistry ().registerFunction (aFunction);
      return aFunction;
    }