fix: change _region to immutable

Author: diegofesanto

Functions/Client.cs

@@ -20,7 +20,7 @@ public partial class Client : IFunctionsClient
     {
         private HttpClient _httpClient = new HttpClient();
         private readonly string _baseUrl;
-        private FunctionRegion _region;
+        private readonly FunctionRegion _region;
 
         /// <summary>
         /// Function that can be set to return dynamic headers.
@@ -128,14 +128,15 @@ private async Task<HttpResponseMessage> HandleRequest(
 
             options.Headers["X-Client-Info"] = Util.GetAssemblyVersion(typeof(Client));
 
-            if (options.FunctionRegion != null)
+            var region = options.FunctionRegion;
+            if (region == null)
             {
-                _region = options.FunctionRegion;
+                region = _region;
             }
 
             if (_region != FunctionRegion.Any)
             {
-                options.Headers["x-region"] = _region.ToString();
+                options.Headers["x-region"] = region.ToString();
             }
 
             var builder = new UriBuilder(url);

Functions/InvokeFunctionOptions.cs

@@ -164,7 +164,7 @@ public bool Equals(FunctionRegion other)
             /// <summary>
             /// Overloading the operator ==
             /// </summary>
-            public static bool operator ==(FunctionRegion left, FunctionRegion right) =>
+            public static bool operator ==(FunctionRegion? left, FunctionRegion? right) =>
                 Equals(left, right);
 
             /// <summary>