将List<T>转化成 DataTable--调整可空类型的转化错误

string cmdText = @"select   * from kb_lable_temp where 1=2";
                using (SqlConnection conn = new SqlConnection(DBCtx.ConnStr))
                {
                      DataTable dt = new DataTable();
                      SqlCommand cmd = new SqlCommand(cmdText,conn);
                      conn.Open();
                      using (var dr = cmd.ExecuteReader(CommandBehavior.SchemaOnly))
                      {
                          dt.Load(dr);
                          dt.WriteXmlSchema("C:\\xxx.xml");
                      }
                      

                }
                DataTable dt3 = new DataTable();
                dt3.ReadXmlSchema("C:\\xxx.xml");

using System.Data;
using System.Collections.Generic;
using System.Reflection;
using System;
using System.Collections;
namespace F.Studio.Util
{
    public static class DataTableExtensions
    {
        /// <summary> 
        /// 转化一个DataTable 
        /// </summary> 
        /// <typeparam name="T"></typeparam> 
        /// <param name="list"></param> 
        /// <returns></returns> 
        public static DataTable ToDataTable<T>(this IEnumerable<T> list,params string[] tableName)
        {
            //创建属性的集合 
            List<PropertyInfo> pList = new List<PropertyInfo>();
            //获得反射的入口 
            Type type = typeof(T);
            string tname = "Table1";
            if (tableName.Length >= 1)
            {
                tname = tableName[0];
            }
            DataTable dt = new DataTable(tname);
            //把所有的public属性加入到集合 并添加DataTable的列 
            Array.ForEach<PropertyInfo>(type.GetProperties(), p =>
            {
                pList.Add(p); 
                var theType=p.PropertyType;
                //处理可空类型
                if (theType.IsGenericType && theType.GetGenericTypeDefinition().Equals(typeof(Nullable<>)))
                {
                    dt.Columns.Add(p.Name,Nullable.GetUnderlyingType(theType));
                }
                else
                {
                    dt.Columns.Add(p.Name, theType);
                }
            });
            foreach (var item in list)
            {
                //创建一个DataRow实例 
                DataRow row = dt.NewRow();
                //给row 赋值 
                pList.ForEach(p =>
                {
                    var v=p.GetValue(item, null);
                    row[p.Name] = v==null ? DBNull.Value : v;
                    
                });
                //加入到DataTable 
                dt.Rows.Add(row);
            }
            return dt;
        }
}
}