sitecore - Server Error "Object reference not set to an instance of an object" after insert from branch -

everything works correctly after sitecore update 7.0 7.2 see following server error when creating site branch

[nullreferenceexception: object reference not set instance of object.]    sitecore.nexus.data.datacommands.addfromtemplatecommand.(item , item , string , id , id , string , safedictionary`2 ) +420    sitecore.nexus.data.datacommands.addfromtemplatecommand.(item , item , string , id , id , string , safedictionary`2 ) +856    sitecore.nexus.data.datacommands.addfromtemplatecommand.(string , item , item , id ) +569    sitecore.data.engines.datacommands.addfromtemplatecommand.doexecute() +113    sitecore.data.engines.enginecommand`2.execute() +121    sitecore.data.engines.dataengine.addfromtemplate(string itemname, id templateid, item destination, id newid) +101    sitecore.data.managers.itemprovider.addfromtemplate(string itemname, id templateid, item destination, id newid) +363    sitecore.data.managers.itemmanager.addfromtemplate(string itemname, id templateid, item destination, id newitemid) +203    sitecore.data.managers.itemmanager.addfromtemplate(string itemname, id templateid, item destination) +286    sitecore.data.items.item.add(string name, branchid branchid) +110    sitecore.workflows.workflowcontext.additem(string name, branchitem branch, item parent) +279    sitecore.shell.framework.commands.addmaster.add(clientpipelineargs args) +803  [targetinvocationexception: exception has been thrown target of invocation.]    system.runtimemethodhandle.invokemethod(object target, object[] arguments, signature sig, boolean constructor) +0    system.reflection.runtimemethodinfo.unsafeinvokeinternal(object obj, object[] parameters, object[] arguments) +76    system.reflection.runtimemethodinfo.invoke(object obj, bindingflags invokeattr, binder binder, object[] parameters, cultureinfo culture) +211    system.reflection.methodbase.invoke(object obj, object[] parameters) +35    sitecore.nexus.pipelines.nexuspipelineapi.resume(pipelineargs args, pipeline pipeline) +398    sitecore.web.ui.sheer.clientpage.resumepipeline() +285    sitecore.web.ui.sheer.clientpage.onprerender(eventargs e) +547    sitecore.shell.applications.contentmanager.contenteditorpage.onprerender(eventargs e) +25    system.web.ui.control.prerenderrecursiveinternal() +113    system.web.ui.page.processrequestmain(boolean includestagesbeforeasyncpoint, boolean includestagesafterasyncpoint) +4297 

a site creates correctly , see no problems there.

as far see error occurs in item:addmaster command:

<command name="item:addmaster" type="sitecore.shell.framework.commands.addmaster,sitecore.kernel" /> 

i have tried decompile sitecore.nexus library without success. after of hours of investigation found error disappears if turn off custom event handler

<event name="item:created">    <handler type="app.client.tasks.itemeventhandler, app.client" method="onitemcreated" /> </event> 

the handler responsible auto mapping configuration settings in new site created branch. technically there item in branch template called mapper , works trigger. last item in branch tree. when admin adds site branch, event handler checks mapper created (in other words site created), runs auto mapping functionality , deletes trigger.

if omit checks, handler looks like

new itemmappingmanager(contextitem, database.getdatabase("master").items[id.parse(mappingconfigurationitemid)]).execute();  // delete trigger item once branch has been created , mapping done using (new securitydisabler()) {     contextitem.delete(); } 

looks changed in sitecore's event model have lack of knowledge here.

try wrapping calls sitecore.data.engines.dataengine.addfromtemplate or calls making add item eventdisabler. because exception being thrown in nexus, it's difficult exact cause of issue is.

when experienced similar issue, had theory there may have been eventing firing , causing exceptions. error did not occur, , difficult find cause of error since being thrown in nexus. while investigating , debugging best (deobfuscated, decompiled , read through , debugged nexus), found there several api calls being made raise events (e.g. addversion, addmaster, etc.). considered theory confirmed when exception disappeared after wrapped code in eventdisabler.

my similar experience

i experienced same issue sitecore 8.1.2. difference between code , code in op leveraging new (i believe newer op) itemprovider via processor have added addfromtemplate pipeline.

the below processor added. use processor run rules, , receiving exact same error, until wrapped call sitecore.data.engines.dataengine.addfromtemplate (must called or else item never gets created) in eventdisabler.

processor before fix

        public override void process([notnull] addfromtemplateargs args)         {             id id;               if (args.aborted                  || string.isnullorwhitespace(rulefolderid)                  || !settings.rules.itemeventhandlers.rulessupported(args.destination.database)                 || !id.tryparse(rulefolderid, out id))             {                 return;             }              assert.hasaccess(args.destination.access.cancreate(), "you not have permission create items here.");              // exception thrown call, required call               //   processor, or else item not created             var item = args.destination.database.engines.dataengine.addfromtemplate(                 args.itemname,                 args.templateid,                 args.destination,                 args.newid);              args.processoritem = item;             args.result = item;              var rulecontext = new pipelineargsrulecontext<addfromtemplateargs>(args);              rulemanager.runrules(rulecontext, id);         } 

processor fix

    public override void process([notnull] addfromtemplateargs args)     {         id id;           if (args.aborted              || string.isnullorwhitespace(rulefolderid)              || !settings.rules.itemeventhandlers.rulessupported(args.destination.database)             || !id.tryparse(rulefolderid, out id))         {             return;         }          assert.hasaccess(args.destination.access.cancreate(), "you not have permission create items here.");          using (new eventdisabler()) // fixes exception nexus         {             var item = args.destination.database.engines.dataengine.addfromtemplate(                 args.itemname,                 args.templateid,                 args.destination,                 args.newid);              args.processoritem = item;             args.result = item;         }          var rulecontext = new pipelineargsrulecontext<addfromtemplateargs>(args);          rulemanager.runrules(rulecontext, id);     } 

additional observations

the error experienced 33% of time , when adding item branch template programmatically (never occurred when adding ui). exact location of error appeared change each time, , not able find source of randomization.