重写BeanUtils，不拷贝空值到对象

/**
     * 拷贝属性，但不适用null替换原属性
     * @param source 源
     * @return String[]
     */
    public static String[] getNullPropertyNames (Object source) {
        final BeanWrapper src = new BeanWrapperImpl(source);
        java.beans.PropertyDescriptor[] pds = src.getPropertyDescriptors();

        Set emptyNames = new HashSet<>();
        for(java.beans.PropertyDescriptor pd : pds) {
            Object srcValue = src.getPropertyValue(pd.getName());
            if (srcValue == null) {
                emptyNames.add(pd.getName());
            }
        }
        String[] result = new String[emptyNames.size()];
        return emptyNames.toArray(result);
    }

    public static void copyPropertiesIgnoreNull(Object src, Object target){
        BeanUtil.copyProperties(src, target, getNullPropertyNames(src));
    }