private RegionScannerHolder checkQuotaAndGetRegionScannerContext(long scannerId) {
    return scanners.get(toScannerName(scannerId));
  }
Returns The associated RegionScannerHolder for <code>scannerId</code> or null.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/RSRpcServices.java