@Override
  public String toString() {
    return "PartitionId: " + partitionId.toPathString() + " in the cloud";
  }
Detects duplicates in {@code keys}
@param keys list of {@link StoreKey} to detect duplicates in
@throws IllegalArgumentException if a duplicate is detected
ambry-cloud/src/main/java/com/github/ambry/cloud/CloudBlobStore.java