public void addSampleNulls(VectorizedRowBatch batch) {
    for (int i = 0; i != batch.numCols; i++) {
      addSampleNulls(batch.cols[i]);
    }
  }
Add null values, but do it faster, by avoiding use of Random().

@param col
ql/src/test/org/apache/hadoop/hive/ql/exec/vector/TestVectorizedRowBatch.java