/**
     * Retrieve a function map containing a pre-configured function
     * mapping.  It must include the following functions.
     * <ul>
     * <li>linq:range</li>
     * <li>linq:repeat</li>
     * <li>linq:_empty</li>
     * </ul>
     * @return A initial map for functions, null if there is none.
     *
     * @since EL 3.0
     */