@Override
  @edu.umd.cs.findbugs.annotations.SuppressWarnings(value = "NP_NULL_ON_SOME_PATH_EXCEPTION",
      justification = "FindBugs seems confused on ps in below.")
  List<RegionInfo> getRegionsOnCrashedServer(MasterProcedureEnv env) {
    // Super will return an immutable list (empty if nothing on this server).
    List<RegionInfo> ris = super.getRegionsOnCrashedServer(env);
    if (!ris.isEmpty()) {
      return ris;
    }
    // Nothing in in-master context. Check for Unknown Server! in hbase:meta.
    // If super list is empty, then allow that an operator scheduled an SCP because they are trying
    // to purge 'Unknown Servers' -- servers that are neither online nor in dead servers
    // list but that ARE in hbase:meta and so showing as unknown in places like 'HBCK Report'.
    // This mis-accounting does not happen in normal circumstance but may arise in-extremis
    // when cluster has been damaged in operation.
    UnknownServerVisitor visitor =
      new UnknownServerVisitor(env.getMasterServices().getConnection(), getServerName());
    try {
      MetaTableAccessor.scanMetaForTableRegions(env.getMasterServices().getConnection(), visitor,
        null);
    } catch (IOException ioe) {
      LOG.warn("Failed scan of hbase:meta for 'Unknown Servers'", ioe);
      return ris;
    }
    // create the server state node too
    env.getAssignmentManager().getRegionStates().createServer(getServerName());
    LOG.info("Found {} mentions of {} in hbase:meta of OPEN/OPENING Regions: {}",
      visitor.getReassigns().size(), getServerName(), visitor.getReassigns().stream()
        .map(RegionInfo::getEncodedName).collect(Collectors.joining(",")));
    return visitor.getReassigns();
  }
If no Regions found in Master context, then we will search hbase:meta for references to the
passed server. Operator may have passed ServerName because they have found references to
'Unknown Servers'. They are using HBCKSCP to clear them out.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/procedure/HBCKServerCrashProcedure.java