title: .NET-Core 3 MVC Controller Url.Action returning null
body: <p>I have the following functions in my controller. I am trying to have the "MethodAsync" create a callback URL to the "CallbackAsync" method.</p>
  
  <p>For thirdPartyCallbackUrl 0 to 3, I get a correct URL. However, for 4 to 7, I get a null value. I can't figure out what is going on.</p>
  
  <pre><code>    [Route("auth")]
      [ApiController]
      public class AuthController : Controller
      {
          [HttpGet("othermethod")]
          public async Task&lt;IActionResult&gt; OtherMethod()
          {
              return Ok();
          }
  
          [HttpGet("third-party-callback")]
          public async Task&lt;IActionResult&gt; CallbackAsync()
          {
              return Ok();
          }
  
          [HttpPost("third-party-login/{loginType}")]
          public async Task&lt;IActionResult&gt; MethodAsync()
          {
              string thirdPartyCallbackUrl = Url.ActionLink(action: nameof(CallbackAsync));
              string thirdPartyCallbackUrl1 = Url.ActionLink(action: nameof(CallbackAsync), controller: "Auth");
              string thirdPartyCallbackUrl2 = Url.ActionLink(action: "CallbackAsync", controller: "Auth");
              string thirdPartyCallbackUrl3 = Url.ActionLink(action: "CallbackAsync");
              string thirdPartyCallbackUr4 = Url.ActionLink(action: nameof(OtherMethod));
              string thirdPartyCallbackUrl5 = Url.ActionLink(action: nameof(OtherMethod), controller: "Auth");
              string thirdPartyCallbackUrl6 = Url.ActionLink(action: "OtherMethod", controller: "Auth");
              string thirdPartyCallbackUrl7 = Url.ActionLink(action: "OtherMethod");
  
              ...
          }
      }
  </code></pre>