code: function removeAdditionOfZero(node) {
    if (node.op !== '+') {
      return Node.Status.noChange(node);
    }
    const zeroIndex = node.args.findIndex(arg => {
      return Node.Type.isConstant(arg) && arg.value === '0';
    });
    let newNode = clone(node);
    if (zeroIndex >= 0) {
      // remove the 0 node
      newNode.args.splice(zeroIndex, 1);
      // if there's only one operand left, there's nothing left to add it to,
      // so move it up the tree
      if (newNode.args.length === 1) {
        newNode = newNode.args[0];
      }
      return Node.Status.nodeChanged(
        ChangeTypes.REMOVE_ADDING_ZERO, node, newNode);
    }
    return Node.Status.noChange(node);
  }
docs: If `node` is an addition node with 0 as one of its operands, remove 0 from the operands list. Returns a Node.Status object.