CompactableOplog[] getOplogToBeCompacted() {
    return getOplogsToBeCompacted(false);
  }
gets the available oplogs to be compacted from the LinkedHashMap

@return Oplog[] returns the array of oplogs to be compacted if present else returns null
geode-core/src/main/java/org/apache/geode/internal/cache/DiskStoreImpl.java