@Override
  public String toString() {
    return "PendingBlocksManager{"
        + "pendingBlocks ["
        + pendingBlocks.values().stream()
            .map(ImmutablePendingBlock::block)
            .map(b -> b.getHeader().getNumber() + " (" + b.getHash() + ")")
            .collect(Collectors.joining(", "))
        + "], pendingBlocksByParentHash="
        + pendingBlocksByParentHash
        + '}';
  }
Get the lowest pending ancestor block saved for a block

@param block target block
@return An optional with the lowest ancestor pending block
ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/sync/state/PendingBlocksManager.java