docs: @Override
      public ChronicleMapBuilder<K, V> averageKey(K averageKey) {
          Objects.requireNonNull(averageKey);
          checkSizeIsStaticallyKnown(keyBuilder, "Key");
          this.averageKey = averageKey;
          sampleKey = null;
          averageKeySize = UNDEFINED_DOUBLE_CONFIG;
          return this;
      }