     *
     * @param propertyPath property name prefixed with an association alias
     * @return Criterion
     */
    protected Criterion createIsNull(String propertyPath) {
        return Restrictions.isNull(propertyPath);
    }
    
    /**
     * Apply a "not equal" constraint to the named property.
     * 
     * @param propertyPath property name prefixed with an association alias
     * @param argument value
     * @return Criterion
     */