docs: public V computeIfAbsent(final int key, final IntFunction<? extends V> mappingFunction)
      {
          V value = getMapped(key);
          if (value == null)
          {
              value = mappingFunction.apply(key);
              if (value != null)
              {
                  put(key, value);
              }
          }
          else
          {
              value = unmapNullValue(value);
          }
  
          return value;
      }