Rethinking BST `Find` method signature

**Describe the bug**
The `Find` method in BinarySearchTree throws exceptions. Semantically, 'Find' and 'Get' are two different methods. My suggestion is to return null in case nothing is found in 'Find' and throw exceptions in a new method 'Get'. I understand that there would be a backwards compatibility issue, but the current state really limits the usage of the method and is unintuitive to use.