@Nullable ImmutableMapEntry<K, V> keyBucketHead,
      boolean throwIfDuplicateKeys)
      throws BucketOverflowException {
    int bucketSize = 0;
    for (; keyBucketHead != null; keyBucketHead = keyBucketHead.getNextInKeyBucket()) {
      if (keyBucketHead.getKey().equals(key)) {
        if (throwIfDuplicateKeys) {
          checkNoConflict(/* safe= */ false, "key", keyBucketHead, key + "=" + newValue);
        } else {