Compiler error with generic Blazor component

Question

I've defined a custom select component in Blazor like this:

public class BetterInputSelect<TItem> : InputBase<TItem>
{
  [Parameter]
  public IEnumerable<TItem> Data { get; set; } = new List<TItem>();

  protected override void BuildRenderTree(RenderTreeBuilder builder)
  {
    builder.OpenElement(0, "select");
    builder.AddMultipleAttributes(1, AdditionalAttributes);
    builder.AddAttribute(2, "class", CssClass);
    builder.AddAttribute(3, "value", BindConverter.FormatValue(CurrentValueAsString));
    builder.AddAttribute(4, "onchange", EventCallback.Factory.CreateBinder<string>(
      this, value => CurrentValueAsString = value, CurrentValueAsString!, null));

    foreach (var item in this.Data)
    {
      builder.OpenElement(5, "option");
      builder.AddAttribute(6, "value", item!.ToString());
      builder.AddContent(7, this.FindDisplayName(item));
      builder.CloseElement();
    }

    builder.CloseElement();
  }

  protected override bool TryParseValueFromString(string? value, out TItem result, out string validationErrorMessage)
  {
    // Check for enums first.
    if (typeof(TItem).IsEnum && BindConverter.TryConvertTo(value, CultureInfo.CurrentCulture, out TItem? parsedValue))
    {
      result = parsedValue!;
      validationErrorMessage = null!;
      return true;
    }

    // Other types here
    // ...

    result = default!;
    validationErrorMessage = $"The {FieldIdentifier.FieldName} field is not valid.";
    return false;
  }

  private string FindDisplayName(TItem value)
  {
    return value switch
    {
      null => string.Empty,
      Enum @enum => @enum.GetDescription(),
      _ => value.ToString() ?? string.Empty
    };
  }
}

which can then be used like this:

<BetterInputSelect Data="@Reasons" @bind-Value="@Reason" />

where Reasons and Reason are defined like this:

public SomeReason Reason { get; set; }

private IEnumerable<SomeReason>? Reasons { get; set; }

...

public enum SomeReason 
{
  ...
}

This works great as long as the value that is bound by @bind-Value is not nullable. When I do:

public SomeReason? Reason { get; set; }

I get a compile time error:

[CS0411] The type arguments for method 
'TypeInference.CreateBetterInputSelect_0<TItem>(RenderTreeBuilder, int, int, IEnumerable<TItem>, int, TItem, int, EventCallback<TItem>, int, Expression<Func<TItem>>)' 
cannot be inferred from the usage. Try specifying the type arguments explicitly.

Can I simply not bind to a nullable property, or is there a way to make the compiler happy that I've missed?

EDIT

And if I try to define the type explicitly like this:

<BetterInputSelect
  Data="@Reasons" 
  @bind-Value="@Reason" 
  TItem="SomeReason" />

then I get the following compiler errors:

[CS1503] Argument 1: cannot convert from 'SomeReason?' to 'SomeReason'
[CS1503] Argument 2: cannot convert from 'Microsoft.AspNetCore.Components.EventCallback<SomeReason?>' to 'Microsoft.AspNetCore.Components.EventCallback'
[CS0266] Cannot implicitly convert type 'SomeReason?' to 'SomeReason'. An explicit conversion exists (are you missing a cast?)
[CS1662] Cannot convert lambda expression to intended delegate type because some of the return types in the block are not implicitly convertible to the delegate return type

Answer 1

The solution was as follows:

In BetterInputSelect<TItem> :

// Was:
//   [Parameter]
//   public IEnumerable<TItem> Data { get; set; } = new List<TItem>();

[Parameter]
public IEnumerable<TItem?> Data { get; set; } = new List<TItem?>();

and in the view I did:

<BetterInputSelect
  Data="@(Reasons as IEnumerable<SomeReason?>)" 
  TItem="SomeReason?"
  @bind-Value="@Reason" />

which works when @Reason is nullable- and non-nullable. The non-nullable would of course not need a cast and explicit type definition:

<BetterInputSelect
  Data="@Reasons" 
  @bind-Value="@Reason" />