code: public V remove(Object key) {
          final int index = indexOfKey(key);
          if (index >= 0) {
              return removeAt(index);
          }
  
          return null;
      }
docs: Remove an existing key from the array map.
  @param key The key of the mapping to remove.
  @return Returns the value that was stored under the key, or null if there
  was no such key.