private RedBlackEntry<K, V> getNode(K key) {
		RedBlackEntry<K, V> node = getEntryLessThanEqual(key);
		if (node != null && node.getKey()
				.equals(key)) {
			return node;
		}
		return null;
	}
Adds the given key,value to the map. If the map does not allow duplicate keys and a key
already exists, the old value will be replaced by the new value and the old value will be
returned. 
@param key the key to add to the set.
@return the old value associated with the key, or null if the key was not previously in the map.
Ghidra/Framework/Generic/src/main/java/ghidra/util/datastruct/RedBlackTree.java