message: Use C++11 nullptr keyword rather than NULL macro
diff: @@ -573,7 +573,7 @@ bool CXThinBlock::HandleMessage(CDataStream &vRecv, CNode *pfrom, std::string st
  }
  CValidationState state;
  - CBlockIndex *pIndex = NULL;
  + CBlockIndex *pIndex = nullptr;
  if (!AcceptBlockHeader(thinBlock.header, state, Params(), &pIndex))
  {
  int nDoS;
  @@ -1434,7 +1434,7 @@ void ConnectToThinBlockNodes()
  // NOTE: Because the only nodes we are connecting to here are the ones the user put in their
  // bitcoin.conf/commandline args as "-connect-thinblock", we don't use the semaphore to limit outbound
  // connections
  - OpenNetworkConnection(addr, false, NULL, strAddr.c_str());
  + OpenNetworkConnection(addr, false, nullptr, strAddr.c_str());
  MilliSleep(500);
  }
  }
  @@ -1460,14 +1460,14 @@ void CheckNodeSupportForThinBlocks()
  bool ClearLargestThinBlockAndDisconnect(CNode *pfrom)
  {
  - CNode *pLargest = NULL;
  + CNode *pLargest = nullptr;
  LOCK(cs_vNodes);
  for (CNode *pnode : vNodes)
  {
  - if ((pLargest == NULL) || (pnode->nLocalThinBlockBytes > pLargest->nLocalThinBlockBytes))
  + if ((pLargest == nullptr) || (pnode->nLocalThinBlockBytes > pLargest->nLocalThinBlockBytes))
  pLargest = pnode;
  }
  - if (pLargest != NULL)
  + if (pLargest != nullptr)
  {
  thindata.ClearThinBlockData(pLargest, pLargest->thinBlock.GetBlockHeader().GetHash());
  pLargest->fDisconnect = true;
  