Error Caught in Page_Error event (BasePage.cs)

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Error in: https://www.bowling-stats.com/Page/League/BowlerStatsSum1.aspx
Error Message: Value cannot be null. Parameter name: String
Stack Trace:
at System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal) at System.Number.ParseInt32(String s, NumberStyles style, NumberFormatInfo info) at Page_League_BowlerStatsSum1.Page_Load(Object sender, EventArgs e) at System.Web.UI.Control.OnLoad(EventArgs e) at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)