private String encodeBytes(byte[] buffer) {
    return buffer == null ? null : Base64.getEncoder().encodeToString(buffer);
  }
Checks whether the column statistics data stores histogram statistics, and returns its base64 encoding if so.
@param cd the column statistics data
@return the base64 encoding of the histogram statistics if existing, null otherwise.
ql/src/java/org/apache/hadoop/hive/ql/exec/DDLPlanUtils.java