c# - NullReferenceException when nothing is null? -

i testing (integration) repository layer , keep getting null reference error ef. concern is, there nothing in object null when run debugger. in fact there nothing in entire method null. of properties set in automapper , using real (not mocked) values everything. there , use real version of code.

test:

[test] public void clone_shouldcloneuser() {     using (var scope = new transactionscope())     {         //arrange         var request = builder<cloneuserrequest>.createnew()             .with(x => x.keytoclone = 29)             .with(x => x.user = builder<user>.createnew().with(y => y.key = 0)                 .build())             .build();          //act         _sut.clone(request);          //assert         assert.doesnotthrow(() => _sut.clone(request));     } } 

method:

public void clone(cloneuserrequest request) {     var usersgroupstobecloned = _context.webusergroups.where(x => x.userkey == request.keytoclone).tolist();     var webuser = _mappingservice.map(request.user, new webuser());     webuser.webusergroups = usersgroupstobecloned;     //on line receive nullreferenceexception, nothing null     _context.webusers.add(webuser);     _context.savechanges(); } 

stack trace:

system.nullreferenceexception : object reference not set instance of object. @ system.data.entity.core.objects.dataclasses.relatedend.markforeignkeypropertiesmodified() @ system.data.entity.core.objects.dataclasses.entityreference.addtonavigationpropertyifcompatible(relatedend otherrelatedend) @ system.data.entity.core.objects.dataclasses.relatedend.includeentity(ientitywrapper wrappedentity, boolean addrelationshipasunchanged, boolean doattach) @ system.data.entity.core.objects.dataclasses.entitycollection`1.include(boolean addrelationshipasunchanged, boolean doattach) @ system.data.entity.core.objects.dataclasses.relationshipmanager.addrelatedentitiestoobjectstatemanager(boolean doattach) @ system.data.entity.core.objects.objectcontext.addobject(string entitysetname, object entity) @ system.data.entity.internal.linq.internalset`1.<>c__displayclassd.<add>b__c() @ system.data.entity.internal.linq.internalset`1.actonset(action action, entitystate newstate, object entity, string methodname) @ system.data.entity.internal.linq.internalset`1.add(object entity) @ system.data.entity.dbset`1.add(tentity entity) @ repositories.userrepository.clone(cloneuserrequest request) in userrepository.cs: line 39 @ repositories.userrepositoryintegrationtests.clone_shouldcloneuser() in userrepositoryintegrationtests.cs: line 50 

is there obvious missing or bug in ef perhaps?

i figured out wrong. our db structure terrible , there circular reference between webusergroup (it has child webuser) , webuser(it has collection of webusergroups). when got of usergroups clone user, had reference user cloning. somehow ef decided send me nullreferenceexception. when changed webuser property on groups new 1 works great. time talk dba's updating this...