android - Realm.io, get NPE when trying to set list to a realm object -


i tried add list of realm objects one, hit npe

        realm.begintransaction();          // add person         person person = realm.createobject(person.class);         person.setid(1);         person.setname(name);          realmlist<cat> listofcats = new realmlist<cat>();         (int = 0; i<10; i++){             cat cat = new cat();             if(i!=5)                 cat.setname("cat "+i);             else                 cat.setname("tung");             listofcats.add(cat);         }         person.setcats(listofcats);          // when write transaction committed, changes synced disk.         realm.committransaction();

the line person.setcats triggers error: 

       java.lang.nullpointerexception: attempt invoke interface method 'long io.realm.internal.row.getindex()' on null object reference

if change code inside for loop: 

       person.getcats().add(cat)

instead of using separate realm list, works, i'm curious why first way doesn't, since writing code in second way seems cumbersome. thanks


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