code: public Object remove(String key) {
  		Object last = null;
  		int index = keys.indexOf(key);
  		if (keys.remove(key)) {
  			last = values.remove(index).value;
  			size--;
  			if (size < 1)
  				isEmpty = true;
  		}
  
  		return last;
  	}
docs: Removes the mapping for a key from this map if it is present More
  formally, if this map contains a mapping from key k to value v such that
  (key==null ? k==null : key.equals(k)), that mapping is removed. (The map
  can contain at most one such mapping.)
  
  @param key
  @return the object that is being removed