private void findNextKeyHashPair() throws IOException {
      boolean hasNext = sourceHashReader.next();
      if (hasNext) {
        nextSourceKey = sourceHashReader.getCurrentKey();
      } else {
        // no more keys - last hash goes to the end
        nextSourceKey = null;
      }
    }
Attempt to read the next source key/hash pair. If there are no more, set nextSourceKey to
null
hbase-mapreduce/src/main/java/org/apache/hadoop/hbase/mapreduce/SyncTable.java