public static byte[] createCompositeKey(byte[] tableName, ImmutableBytesWritable suffix) {
    return combineTableNameSuffix(tableName, suffix.get());
  }
Alternate api which accepts an ImmutableBytesWritable for the suffix
@see MultiTableHFileOutputFormat#createCompositeKey(byte[], byte[])
hbase-mapreduce/src/main/java/org/apache/hadoop/hbase/mapreduce/MultiTableHFileOutputFormat.java