title: Custom Blazor DateTime using inherits InputBase<DateTime> with ValidationMessage
body: <p>I have the following custom date input:</p>
  <h4>CustomDateInput.razor</h4>
  <pre><code>&lt;input type=&quot;date&quot;
           class=&quot;@CssClass&quot;
           @bind=CurrentValue
           @attributes=AdditionalAttributes /&gt;
  
  @if (ValidationFor is not null)
  {
      &lt;ValidationMessage For=&quot;@ValidationFor&quot; /&gt;
  }
  
  @using System.Linq.Expressions
  @inherits InputBase&lt;DateTime?&gt;
  
  @code {
      [Parameter] public Expression&lt;Func&lt;DateTime&gt;&gt;? ValidationFor { get; set; }
  
      protected override bool TryParseValueFromString(string? value, out DateTime? result, out string validationErrorMessage)
      {
          result = CurrentValue;
          validationErrorMessage = &quot;&quot;;
          return true;
      }
  }
  </code></pre>
  <h4>FooPage.razor</h4>
  <pre><code>&lt;CustomInputDate @bind-Value=&quot;FooDate&quot; ValidationFor=&quot;() =&gt; FooDate&quot;&gt;&lt;/CustomInputDate&gt;
  </code></pre>
  <h4>FooPage.razor.cs</h4>
  <pre class="lang-cs prettyprint-override"><code>public DateTime? FooDate { get; set; }
  </code></pre>
  <p>However, I get errors:</p>
  <p><img src="https://user-images.githubusercontent.com/812974/125317868-5416f900-e307-11eb-83d4-c3869c951295.png" alt="image" /></p>
  <p>How can I modify my <code>CustomDateInput</code> to allow for a Validation parameter to show a ValidationMessage?</p>