# lastKeyBefore method

K lastKeyBefore (K key)

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

## Implementation

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