Btw fix the repeatedly added agent header

Assign the Expected100 header only if the provided value is not null

Author: alexeyzimarev

src/RestSharp/RestClient.cs

@@ -125,8 +125,11 @@ public RestClient(HttpMessageHandler handler, bool disposeHandler = true) : this
 
     void ConfigureHttpClient(HttpClient httpClient) {
         if (Options.MaxTimeout > 0) httpClient.Timeout = TimeSpan.FromMilliseconds(Options.MaxTimeout);
-        httpClient.DefaultRequestHeaders.UserAgent.ParseAdd(Options.UserAgent);
-        httpClient.DefaultRequestHeaders.ExpectContinue = Options.Expect100Continue;
+        if (httpClient.DefaultRequestHeaders.UserAgent.All(x => x.Product.Name != "RestSharp")) {
+            httpClient.DefaultRequestHeaders.UserAgent.ParseAdd(Options.UserAgent);
+        }
+        if (Options.Expect100Continue != null)
+            httpClient.DefaultRequestHeaders.ExpectContinue = Options.Expect100Continue;
     }
 
     void ConfigureHttpMessageHandler(HttpClientHandler handler) {

src/RestSharp/RestClientOptions.cs

@@ -70,20 +70,20 @@ public RestClientOptions(string baseUrl) : this(new Uri(Ensure.NotEmptyString(ba
     /// </summary>
     public X509CertificateCollection? ClientCertificates { get; set; }
 
-    public IWebProxy?               Proxy           { get; set; }
-    public CacheControlHeaderValue? CachePolicy     { get; set; }
-    public bool                     FollowRedirects { get; set; } = true;
+    public IWebProxy?               Proxy             { get; set; }
+    public CacheControlHeaderValue? CachePolicy       { get; set; }
+    public bool                     FollowRedirects   { get; set; } = true;
     public bool?                    Expect100Continue { get; set; } = null;
-    public CookieContainer?         CookieContainer { get; set; }
-    public string                   UserAgent       { get; set; } = DefaultUserAgent;
-    
+    public CookieContainer?         CookieContainer   { get; set; }
+    public string                   UserAgent         { get; set; } = DefaultUserAgent;
+
     /// <summary>
     /// Maximum request duration in milliseconds. When the request timeout is specified using <seealso cref="RestRequest.Timeout"/>,
     /// the lowest value between the client timeout and request timeout will be used.
     /// </summary>
-    public int                      MaxTimeout      { get; set; }
-    
-    public Encoding                 Encoding        { get; set; } = Encoding.UTF8;
+    public int MaxTimeout { get; set; }
+
+    public Encoding Encoding { get; set; } = Encoding.UTF8;
 
     [Obsolete("Use MaxTimeout instead")]
     public int Timeout {
@@ -129,4 +129,4 @@ public int Timeout {
     /// This properly allows to override the default behavior.
     /// </summary>
     public bool AllowMultipleDefaultParametersWithSameName { get; set; }
-}
+}