Null data column returns input string was not in a correct format error

Question

I am working on an event calendar in which time values (start, end) are not always required and are often Null. I'd like the format for times that are entered to read hh:mm tt. I have the code check for null values using the following if statement:

<td>
    @If item.StartTime IsNot Nothing Then
        @item.StartTime.ToString("h:mm tt")
    Else
        @Html.DisplayFor(Function(modelItem) item.StartTime)
    End If
</td>

I still get the following error espite the if statement:

[FormatException: Input string was not in a correct format.]
Microsoft.VisualBasic.CompilerServices.Conversions.ParseDouble(String Value, NumberFormatInfo NumberFormat) +224
Microsoft.VisualBasic.CompilerServices.Conversions.ToInteger(String Value) +92

[InvalidCastException: Conversion from string "h:mm tt" to type 'Integer' is not valid.]
Microsoft.VisualBasic.CompilerServices.Conversions.ToInteger(String Value) +248
ASP._Page_Views_EaglesEvents_Index_vbhtml.Execute() in C:\Users\Iluvw\Documents\Visual Studio 2017\Projects\MVC Projects\Eagles3555\Eagles3555\Views\EaglesEvents\Index.vbhtml:49
System.Web.WebPages.WebPageBase.ExecutePageHierarchy() +197
System.Web.Mvc.WebViewPage.ExecutePageHierarchy() +105
System.Web.WebPages.StartPage.RunPage() +17
System.Web.WebPages.StartPage.ExecutePageHierarchy() +73
System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage) +78
System.Web.Mvc.RazorView.RenderView(ViewContext viewContext, TextWriter writer, Object instance) +235
System.Web.Mvc.BuildManagerCompiledView.Render(ViewContext viewContext, TextWriter writer) +107
System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context) +291
System.Web.Mvc.ControllerActionInvoker.InvokeActionResult(ControllerContext controllerContext, ActionResult actionResult) +13
System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult) +56
System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult) +420
System.Web.Mvc.ControllerActionInvoker.InvokeActionResultWithFilters(ControllerContext controllerContext, IList`1 filters, ActionResult actionResult) +52
System.Web.Mvc.Async.<>c__DisplayClass3_6.<BeginInvokeAction>b__4() +198
System.Web.Mvc.Async.<>c__DisplayClass3_1.<BeginInvokeAction>b__1(IAsyncResult asyncResult) +100
System.Web.Mvc.Async.WrappedAsyncResult`1.CallEndDelegate(IAsyncResult asyncResult) +10
System.Web.Mvc.Async.WrappedAsyncResultBase`1.End() +48
System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeAction(IAsyncResult asyncResult) +27
System.Web.Mvc.<>c.<BeginExecuteCore>b__152_1(IAsyncResult asyncResult, ExecuteCoreState innerState) +11
System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +29
System.Web.Mvc.Async.WrappedAsyncResultBase`1.End() +48
System.Web.Mvc.Controller.EndExecuteCore(IAsyncResult asyncResult) +45
System.Web.Mvc.<>c.<BeginExecute>b__151_2(IAsyncResult asyncResult, Controller controller) +13
System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +22
System.Web.Mvc.Async.WrappedAsyncResultBase`1.End() +48
System.Web.Mvc.Controller.EndExecute(IAsyncResult asyncResult) +26
System.Web.Mvc.Controller.System.Web.Mvc.Async.IAsyncController.EndExecute(IAsyncResult asyncResult) +10
System.Web.Mvc.<>c.<BeginProcessRequest>b__20_1(IAsyncResult asyncResult, ProcessRequestState innerState) +28
System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +29
System.Web.Mvc.Async.WrappedAsyncResultBase`1.End() +48
System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +28
System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +9
System.Web.<>c__DisplayClass7_0.<InvokeEndHandler>b__0() +32
System.Web.StepInvoker.Invoke(Action executionStep) +107
System.Web.<>c__DisplayClass4_0.<Invoke>b__0() +23
Microsoft.AspNet.TelemetryCorrelation.TelemetryCorrelationHttpModule.OnExecuteRequestStep(HttpContextBase context, Action step) +64
System.Web.<>c__DisplayClass284_0.<OnExecuteRequestStep>b__0(Action nextStepAction) +56
System.Web.StepInvoker.Invoke(Action executionStep) +91
System.Web.CallHandlerExecutionStep.InvokeEndHandler(IAsyncResult ar) +123
System.Web.CallHandlerExecutionStep.OnAsyncHandlerCompletion(IAsyncResult ar) +128

The line highlighted in red is @item.StartTime.ToString("h:mm tt"). What did I do wrong?

EDIT: My model code for the time fields:

<Display(Name:="Date")>
<DisplayFormat(DataFormatString:="{0:yyyy-MM-dd}", ApplyFormatInEditMode:=True)>
<DataType(DataType.Date)>
Public Property EventDate As DateTime
<Display(Name:="Start Time")>
<DisplayFormat(DataFormatString:="{0:hh:mm:ss}", ApplyFormatInEditMode:=True)>
<DataType(DataType.Time)>
Public Property StartTime As DateTime?

Answer 1

The reason for the exception is that you are using a Nullable DateTime which does not have a ToString() method that accepts a format string. If you are first doing a null check then you can address this by performing the ToString() on the Value of the Nullable which will be the DateTime:

@If item.StartTime IsNot Nothing Then
        @item.StartTime.Value.ToString("h:mm tt")
// ...