code.aload().setParam(0);
code.putfield().setField(elementType);
// create change tracker and set it
code.iload().setParam(2);
JumpInstruction ifins = code.ifeq();
code.aload().setLocal(ret);
code.anew().setType(CollectionChangeTrackerImpl.class);
code.dup();
code.aload().setLocal(ret);
code.constant().setValue(allowsDuplicates(type));