Fixes #2288

Author: alexeyzimarev

src/RestSharp/Parameters/UrlSegmentParameter.cs

@@ -28,10 +28,10 @@ public partial record UrlSegmentParameter : NamedParameter {
     /// <param name="value">Parameter value</param>
     /// <param name="encode">Optional: encode the value, default is true</param>
     /// <param name="replaceEncodedSlash">Optional: whether to replace all %2f and %2F in the parameter value with '/', default is true</param>
-    public UrlSegmentParameter(string name, string value, bool encode = true, bool replaceEncodedSlash = true)
+    public UrlSegmentParameter(string name, string? value, bool encode = true, bool replaceEncodedSlash = true)
         : base(
             name,
-            value.IsEmpty() ? value : replaceEncodedSlash ? RegexPattern.Replace(value, "/") : value,
+            value.IsEmpty() ? string.Empty : replaceEncodedSlash ? RegexPattern.Replace(value, "/") : value,
             ParameterType.UrlSegment,
             encode
         ) { }

src/RestSharp/Request/RestRequestExtensions.Url.cs

@@ -15,28 +15,27 @@
 namespace RestSharp;
 
 public static partial class RestRequestExtensions {
-    
     /// <summary>
     /// Adds a URL segment parameter to the request. The resource URL must have a placeholder for the parameter for it to work.
     /// For example, if you add a URL segment parameter with the name "id", the resource URL should contain {id} in its path.
     /// </summary>
     /// <param name="request">Request instance</param>
-    /// <param name="name">Name of the parameter, must be matching a placeholder in the resource URL as {name}</param>
+    /// <param name="name">Name of the parameter; must be matching a placeholder in the resource URL as {name}</param>
     /// <param name="value">Value of the parameter</param>
     /// <param name="encode">Encode the value or not, default true</param>
     /// <returns></returns>
-    public static RestRequest AddUrlSegment(this RestRequest request, string name, string value, bool encode = true)
+    public static RestRequest AddUrlSegment(this RestRequest request, string name, string? value, bool encode = true)
         => request.AddParameter(new UrlSegmentParameter(name, value, encode));
 
     /// <summary>
     /// Adds a URL segment parameter to the request. The resource URL must have a placeholder for the parameter for it to work.
     /// For example, if you add a URL segment parameter with the name "id", the resource URL should contain {id} in its path.
     /// </summary>
     /// <param name="request">Request instance</param>
-    /// <param name="name">Name of the parameter, must be matching a placeholder in the resource URL as {name}</param>
+    /// <param name="name">Name of the parameter; must be matching a placeholder in the resource URL as {name}</param>
     /// <param name="value">Value of the parameter</param>
     /// <param name="encode">Encode the value or not, default true</param>
     /// <returns></returns>
     public static RestRequest AddUrlSegment<T>(this RestRequest request, string name, T value, bool encode = true) where T : struct
-        => request.AddUrlSegment(name, Ensure.NotNull(value.ToString(), nameof(value)), encode);
+        => request.AddUrlSegment(name, value.ToString(), encode);
 }

src/RestSharp/Request/UriExtensions.cs

@@ -68,7 +68,7 @@ params ParametersCollection[] parametersCollections
             builder.Path = builder.Path.UrlDecode().Replace(paramPlaceHolder, paramValue);
         }
 
-        return new UrlSegmentParamsValues(builder.Uri, assembled);
+        return new(builder.Uri, assembled);
     }
 }
 

test/RestSharp.Tests/UrlBuilderTests.Get.cs

@@ -62,8 +62,7 @@ public void GET_with_empty_request_and_query_parameters_without_encoding() {
 
     [Fact]
     public void GET_with_Invalid_Url_string_throws_exception()
-        => Assert.Throws<UriFormatException>(
-            () => { _ = new RestClient("invalid url"); }
+        => Assert.Throws<UriFormatException>(() => { _ = new RestClient("invalid url"); }
         );
 
     [Fact]
@@ -107,7 +106,12 @@ public void GET_with_multiple_instances_of_same_key() {
     [Fact]
     public void GET_with_resource_containing_null_token() {
         var request = new RestRequest($"/{Resource}/{{foo}}");
-        Assert.Throws<ArgumentNullException>(() => request.AddUrlSegment("foo", null!));
+        request.AddUrlSegment("foo", null);
+
+        using var client = new RestClient(new Uri(Base));
+
+        var output = client.BuildUri(request);
+        Assert.Equal(new($"{Base}/{Resource}/"), output);
     }
 
     [Fact]