#vulnerable code 
                              Node tryFoldFor(Node n) {
    Preconditions.checkArgument(n.getType() == Token.FOR);
    // This is not a FOR-IN loop
    if (n.getChildCount() != 4) {
      return n;
    }
    // There isn't an initializer
    if (n.getFirstChild().getType() != Token.EMPTY) {
      return n;
    }

    Node cond = NodeUtil.getConditionExpression(n);
    if (NodeUtil.getBooleanValue(cond) != TernaryValue.FALSE) {
      return n;
    }

    NodeUtil.redeclareVarsInsideBranch(n);
    NodeUtil.removeChild(n.getParent(), n);
    reportCodeChange();
    return null;
  } 
                            #location 13 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                              Node tryOptimizeBlock(Node n) {
    // Remove any useless children
    for (Node c = n.getFirstChild(); c != null; ) {
      Node next = c.getNext();  // save c.next, since 'c' may be removed
      if (!mayHaveSideEffects(c)) {
        // TODO(johnlenz): determine what this is actually removing. Candidates
        //    include: EMPTY nodes, control structures without children
        //    (removing infinite loops), empty try blocks.  What else?
        n.removeChild(c);  // lazy kids
        reportCodeChange();
      } else {
        tryOptimizeConditionalAfterAssign(c);
      }
      c = next;
    }

    if (n.isSyntheticBlock() ||  n.getParent() == null) {
      return n;
    }

    // Try to remove the block.
    if (NodeUtil.tryMergeBlock(n)) {
      reportCodeChange();
      return null;
    }

    return n;
  }