code: @Override
      public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) {
          // This might look like a Double Checked Idiom (which is broken), but it is not
          // because value is not a global variable
          V value = get(key);
          if (value != null) {
              return value;
          }
          return super.computeIfAbsent(key, mappingFunction);
      }
docs: An overridden implementation that heavily favors read access over write access speed.
  This is thread-safe.
  
  {@inheritDoc}