c# - Create Users and Roles in ASP.NET 6 & Entity Framework 7 -

i need create users , roles @ first startup of web application. that, write code configure() function in startup.cs.

when run application, error:

an exception of type 'system.aggregateexception' occurred in mscorlib.dll not handled in user code @ call of first function "createusers"

code:

 public async void configure(iapplicationbuilder app, ihostingenvironment env, iloggerfactory loggerfactory, iserviceprovider serviceprovider, applicationdbcontext context) {    ...         await createusers(context, serviceprovider);         await createroles(context, serviceprovider);     }      private async task createusers(applicationdbcontext context, iserviceprovider serviceprovider)     {         list<applicationuser> users = new list<applicationuser>();         users.add(new applicationuser { username = "devuser", email = "dev@dev.com", lastname = "dev", firstname = "dev", passwordhash = "devpassword" });         users.add(new applicationuser { username = "workuser", email = "work@work.com", lastname = "work", firstname = "work", passwordhash = "workpassword" });          foreach(var user in users)         {             var userexist = await _usermanager.findbyemailasync(user.email);             if(userexist != null)             {                 await _usermanager.createasync(user, user.passwordhash);                 context.users.add(user);                 context.savechanges();             }         }     }      private async task createroles(applicationdbcontext context, iserviceprovider serviceprovider)     {         var usermanager = serviceprovider.getrequiredservice<usermanager<applicationuser>>();         var rolemanager = serviceprovider.getrequiredservice<rolemanager<identityrole>>();          list<identityrole> roles = new list<identityrole>();         roles.add(new identityrole { name = "developer", normalizedname = "developer" });         roles.add(new identityrole { name = "work", normalizedname = "work" });         roles.add(new identityrole { name = "admin", normalizedname = "admin" });         roles.add(new identityrole { name = "redacteur", normalizedname = "redacteur" });         roles.add(new identityrole { name = "correcteur", normalizedname = "correcteur" });         roles.add(new identityrole { name = "membre", normalizedname = "membre" });          foreach(var role in roles)         {             var roleexist = await rolemanager.roleexistsasync(role.name);             if(!roleexist)             {                 context.roles.add(role);                 context.savechanges();             }         }          var devuser = await usermanager.findbyemailasync("dev@dev.com");         await usermanager.addtoroleasync(devuser, "developer");         var work = await usermanager.findbyemailasync("work@work.com");         await usermanager.addtoroleasync(work, "work");     }