#vulnerable code 
                              @Override
  public boolean shouldTraverse(NodeTraversal t, Node n, Node parent) {
    if (n.isScript()) {
      this.inExterns = n.getStaticSourceFile().isExtern();
    }
    return true;
  } 
                            #location 4 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                              @Override
  public boolean shouldTraverse(NodeTraversal t, Node n, Node parent) {
    return true;
  }