protected override void RequestHeadersConfigurator(HttpRequestHeaders requestHeaders)
 {
     if (string.IsNullOrWhiteSpace(_token) == false)
     {
         requestHeaders.WithBearerToken(_token);
     }
 }
 public void WithBearerTokenShouldNotValidateParameters(HttpRequestHeaders headers, string token)
 {
     Assert.Throws <ArgumentNullException>(() => headers.WithBearerToken(token));
 }