Potential NPE in ReferenceCountedACLCache#deserialize

Inspired by ZK-3006 , I develop a simple static analysis tool to find other Potential NPE like ZK-3006. This bug is found by this tool ,and I have carefully studied it.  But i am a newbie at here so i may be wrong, hope someone could confirm it and help me improve this tool.

Bug describtion:

callee BinaryInputArchive#startVector will return null:

// code placeholder
public Index startVector(String tag) throws IOException {
    int len = readInt(tag);
     if (len == -1) {
     return null;
}

and caller ReferenceCountedACLCache#deserialize  call it without null check

// code placeholder
Index j = ia.startVector("acls");
while (!j.done()) {
  ACL acl = new ACL();
  acl.deserialize(ia, "acl");
}

but all the other 14 caller of BinaryInputArchive#startVector performs null checker like:

// code placeholder
Index vidx1 = a_.startVector("acl");
  if (vidx1!= null)
     for (; !vidx1.done(); vidx1.incr()){
     .....
    }
   }
}

so i think we also need add null check in caller ReferenceCountedACLCache#deserialize  just like other 14 caller