diff --git a/framework/src/Volo.Abp.Http.Client/Volo/Abp/Http/Client/DynamicProxying/UrlBuilder.cs b/framework/src/Volo.Abp.Http.Client/Volo/Abp/Http/Client/DynamicProxying/UrlBuilder.cs
index 4d77423c7f..78747dd6b0 100644
--- a/framework/src/Volo.Abp.Http.Client/Volo/Abp/Http/Client/DynamicProxying/UrlBuilder.cs
+++ b/framework/src/Volo.Abp.Http.Client/Volo/Abp/Http/Client/DynamicProxying/UrlBuilder.cs
@@ -139,7 +139,7 @@ namespace Volo.Abp.Http.Client.DynamicProxying
                 return dateTimeValue.ToUniversalTime().ToString("O");
             }
 
-            return value.ToString();
+            return value?.ToString();
         }
     }
 }