<EditForm Model="cust" OnSubmit="HandleSubmit">
    <InputNumber @bind-Value="@(this.Id == null? this.idNuM :cust._nunuy)" class="form-control"></InputNumber>
</EditForm>

I get this error:

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

The type arguments for method 'RuntimeHelpers.CreateInferredEventCallback(object, Action, T)' cannot be inferred from the usage. Try specifying the type arguments explicitly.

I tried it:

<EditForm Model="cust" OnSubmit="HandleSubmit">
    <InputNumber @bind-Value="@(this.Id == null? (ulong)this.idNuM : (long)cust._nunuy)" class="form-control"></InputNumber>
</EditForm>