@Override
  public void positionToFirst() {
    seriesPosition = 0;

    currentLogical = 0;
    currentDuplicateCount = duplicateCounts[0];
    currentIsAllNull = seriesIsAllNull[0];

    if (!currentIsAllNull) {
      nonNullKeyPosition = 0;
      currentHashCode = hashCodes[0];
      setNextNonNullKey(0);
    } else {
      nonNullKeyPosition = -1;
    }
    Preconditions.checkState(currentDuplicateCount > 0);
  }
Implementation of when a one key series or a serialized key series is being presented.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/keyseries/VectorKeySeriesSingleImpl.java