diff --git a/IRaCIS.Core.Application/Service/TrialSiteUser/TrialSiteService.cs b/IRaCIS.Core.Application/Service/TrialSiteUser/TrialSiteService.cs
index ba6f9c7ed..ead20906e 100644
--- a/IRaCIS.Core.Application/Service/TrialSiteUser/TrialSiteService.cs
+++ b/IRaCIS.Core.Application/Service/TrialSiteUser/TrialSiteService.cs
@@ -111,7 +111,7 @@ namespace IRaCIS.Core.Application.Services
         }
 
 
-        public async Task<List<TrialSiteSelect>> GetTrialSiteSelectList(string siteName)
+        public async Task<List<TrialSiteSelect>> GetTrialSiteSelectList(string? siteName)
         {
            var list= _siteRepository
                 .WhereIf(!string.IsNullOrWhiteSpace(siteName), t => t.SiteName.Contains(siteName) || t.SiteNameCN.Contains(siteName) || t.AliasName.Contains(siteName))