在调用自定义模型时出现如下错误：求xiyou帮忙看看，这个错误是什么意思
Server Error in '/' Application.
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Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.
Source Error:
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.
Stack Trace:
[NullReferenceException: Object reference not set to an instance of an object.]
PageAdmin.lanmu_zdymodel.979LhvYFk(String , String , String ) +432
PageAdmin.lanmu_zdymodel.m4PH4LJvE() +1520
PageAdmin.lanmu_zdymodel.Page_Load(Object sender, EventArgs e) +133
System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) +15
System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +34
System.Web.UI.Control.OnLoad(EventArgs e) +99
System.Web.UI.Control.LoadRecursive() +47
System.Web.UI.Control.LoadRecursive() +131
System.Web.UI.Control.LoadRecursive() +131
System.Web.UI.Control.LoadRecursive() +131
System.Web.UI.Control.LoadRecursive() +131
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1061
