Handle the case where currentLanguage is null.

framework/src/Volo.Abp.AspNetCore.Mvc.UI.Theme.Basic/Themes/Basic/Components/Toolbar/LanguageSwitch/LanguageSwitchViewComponent.cs

@@ -1,7 +1,9 @@
-using System.Globalization;
+using System.Globalization;
 using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.RequestLocalization;
+using Microsoft.Extensions.DependencyInjection;
 using Volo.Abp.Localization;
 
 namespace Volo.Abp.AspNetCore.Mvc.UI.Theme.Basic.Themes.Basic.Components.Toolbar.LanguageSwitch
@@ -23,12 +25,32 @@ namespace Volo.Abp.AspNetCore.Mvc.UI.Theme.Basic.Themes.Basic.Components.Toolbar
                 CultureInfo.CurrentUICulture.Name
             );
 
+            if (currentLanguage == null)
+            {
+                var abpRequestLocalizationOptionsProvider = HttpContext.RequestServices.GetRequiredService<IAbpRequestLocalizationOptionsProvider>();
+                var localizationOptions = await abpRequestLocalizationOptionsProvider.GetLocalizationOptionsAsync();
+                if (localizationOptions.DefaultRequestCulture != null)
+                {
+                    currentLanguage = new LanguageInfo(
+                        localizationOptions.DefaultRequestCulture.Culture.Name,
+                        localizationOptions.DefaultRequestCulture.UICulture.Name,
+                        localizationOptions.DefaultRequestCulture.UICulture.DisplayName);
+                }
+                else
+                {
+                    currentLanguage = new LanguageInfo(
+                        CultureInfo.CurrentCulture.Name,
+                        CultureInfo.CurrentUICulture.Name,
+                        CultureInfo.CurrentUICulture.DisplayName);
+                }
+            }
+
             var model = new LanguageSwitchViewComponentModel
             {
                 CurrentLanguage = currentLanguage,
                 OtherLanguages = languages.Where(l => l != currentLanguage).ToList()
             };
-            
+
             return View("~/Themes/Basic/Components/Toolbar/LanguageSwitch/Default.cshtml", model);
         }
     }