/// <summary>
/// 获取ModelState的第一个错误信息
/// </summary>
/// <param name="modelState">modelState</param>
/// <returns></returns>
private static string FirstErrorMessage(this ModelStateDictionary modelState)
{
if (modelState == null || modelState.ErrorCount == 0)
{
return(null);
}
return(modelState.FirstModelErrorMessage());
}