@return the next key, null if no match or at end
@param key the key to search for next from
file : https_github_com_apache_commons-collections_git/src/main/java/org/apache/commons/collections4/bidimap/TreeBidiMap.java
file : https_github_com_apache_commons-collections_git/src/main/java/org/apache/commons/collections4/OrderedMap.java