add fix for array

Author: BenjaminAbt

src/MyCSharp.HttpClientHints.AspNetCore/HttpClientHintsRegistration.cs

@@ -57,9 +57,10 @@ public static IServiceCollection AddHttpClientHints(this IServiceCollection serv
             headers.Add("Sec-CH-UA-Mobile");
         }
 
-        if (!string.IsNullOrEmpty(httpClientHintsConfig.Additional))
+        // customization
+        if (httpClientHintsConfig.Additional is not null)
         {
-            headers.Add(httpClientHintsConfig.Additional);
+            headers.AddRange(httpClientHintsConfig.Additional);
         }
 
         // register middleware config

tests/MyCSharp.HttpClientHints.AspNetCore.UnitTests/HttpClientHintsRegistrationTests.cs

@@ -71,15 +71,15 @@ public void AddHttpClientHints_CustomAdditionalHeader_RegistersAdditionalHeader(
     {
         // Arrange
         ServiceCollection services = new();
-        const string customHeader = "X-Custom-Header";
+        string[] customHeaders = ["X-Custom-Header"];
 
         // Act
-        services.AddHttpClientHints(options => options.Additional = customHeader);
+        services.AddHttpClientHints(options => options.Additional = customHeaders);
         ServiceProvider serviceProvider = services.BuildServiceProvider();
         HttpClientHintsMiddlewareConfig options = serviceProvider.GetRequiredService<IOptions<HttpClientHintsMiddlewareConfig>>().Value;
 
         // Assert
-        Assert.Contains(customHeader, options.ResponseHeader);
+        Assert.Contains("X-Custom-Header", options.ResponseHeader);
     }
 
     [Fact]