Update src/c#/GeneralUpdate.Core/GeneralUpdateBootstrap.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: JusterZhu

src/c#/GeneralUpdate.Core/GeneralUpdateBootstrap.cs

@@ -108,9 +108,8 @@ public GeneralUpdateBootstrap SetFieldMappings(Dictionary<string, string> fieldM
             return this;
         }
 
-        public GeneralUpdateBootstrap SetCustomSkipOption(Func<bool> func)
+        public GeneralUpdateBootstrap SetCustomSkipOption(Func<bool>? func)
         {
-            Debug.Assert(func != null);
             _customSkipOption = func;
             return this;
         }