java - Not Able to Access Testcases Under Testplan Using OTA -

i tried writing code getting null pointer exception. tried multiple solutions not able figure out problem. appreciated.

my flow of execution : subject -> test -> tc1(testcase)

itestsettreemanager treemanagerplan =      qcconnection.testsettreemanager().queryinterface(itestsettreemanager.class); itestsetfolder basefolderplan =      treemanagerplan.root().queryinterface(itestsetfolder.class); string foldernamesplan[] = null; testsetfolderplan=null;  if(strtestplanpath.contains("\\")) {     foldernamesplan = strtestplanpath.split("\\\\");     for(int i=1;i<foldernamesplan.length;i++)     {          system.out.println("qc folder parsing.." + foldernamesplan[i]);          if(!foldernamesplan[i].equals(""))         {             boolean createfolder = true;              for(int f=0; f< basefolderplan.count(); f++)             {                 try{                     if(basefolderplan.findchildnode(foldernamesplan[i]).name().equalsignorecase(foldernamesplan[i]))                     {                         createfolder=false;                          break;                     }                 }catch(exception ex)                 {                                                    system.out.println("not able access folder");                 }             }             testsetfolderplan = treemanagerplan.nodebyid(basefolderplan.findchildnode(foldernamesplan[i]).nodeid()).queryinterface(itestsetfolder.class);             basefolderplan=testsetfolderplan;                                system.out.println("basefolder>>>>>>>>>>>>>>>>"+basefolderplan.name());                   itestfactory itestfactory = qcconnection.testfactory().queryinterface(itestfactory.class);             ibasefactory testfactory = tstest.tstestfactory().queryinterface(ibasefactory.class);               ilist tststlist = testfactory.newlist("");             string tsname = null;             for(com4jobject obj4:tststlist)              {                  itstest tstest = obj4.queryinterface(itstest.class);                  tsname=(string) tstest.testid();//.name();                 system.out.println("testcase description "+tstest.name()+"\n qc id : "+ tsname);             }      //        ilist testinstances = testfactory.newlist("");                com4jobject comobjtest = itestfactory.item(tsname);             itest itest = comobjtest.queryinterface(itest.class);             com4jobject subjectfield = (com4jobject)itest.field("ts_subject");             isubjectnode subfolder = subjectfield.queryinterface(isubjectnode.class);             system.out.println(subfolder.name());      /*      isubjectnode node = qcconnection.testfactory().queryinterface(isubjectnode.class);             system.out.println(node.name());             ilist list = node.newlist();             (com4jobject isys : list) {                 system.out.println("test folder : "+ isys.queryinterface(isystreenode.class).name());                        }*/         }