public V remove(Object key) {
        V result = getMap().remove(key);
        insertOrder.remove(key);
        return result;
    }
Gets the previous key to the one specified using insert order.
This method performs a list search to find the key and is O(n).

@param key the key to find previous for
@return the previous key, null if no match or at start
jphp-runtime/src/php/runtime/common/collections/map/ListOrderedMap.java