# firstKeyAfter method

K firstKeyAfter (K key)

Get the first key in the map that is strictly larger than `key`. Returns `null` if no key was not found.

## Implementation

    K firstKeyAfter(K key) {
      if (key == null) throw ArgumentError(key);
      if (_root == null) return null;
      int comp = _splay(key);
      if (comp > 0) return _root.key;
      _SplayTreeNode<K> node = _root.right;
      if (node == null) return null;
      while (node.left != null) {
        node = node.left;
      }
      return node.key;
    }