code: @Override
  	public M filter(BiPredicate<? super K, ? super V> filter) {
  		MapBuilder<K, V, M> builder = builder();
  		for (java.util.Map.Entry<K, V> entry : entrySet()) {
  			if(filter.test(entry.getKey(), entry.getValue())) {
  				builder.put(entry.getKey(), entry.getValue());
  			}
  		}
  		return builder.build();
  	}
docs: ========== NEW F METHODS =========