code: public static JavaRDD<List<List<Writable>>> zeroMeanUnitVarianceSequence(Schema schema,
                      JavaRDD<List<List<Writable>>> sequence) {
          return zeroMeanUnitVarianceSequence(schema, sequence, null);
      }
docs: Normalize the sequence by zero mean unit variance
  
  @param schema   Schema of the data to normalize
  @param sequence Sequence data
  @return Normalized sequence