public String getBlobIds() {
    // BlobId is in base64 format, "," character is not allowed in base64 encoding.
    return blobVersions.stream().map(BlobVersion::getBlobId).reduce((a, b) -> a + "," + b).orElse("");
  }
Return the list of blob ids that were deleted in a comma separated string. If there is no blob ids, then
an empty string would be returned.
@return
ambry-api/src/main/java/com/github/ambry/named/DeleteResult.java