void zeroOutBlobContent(int index) {
    byte[] zeroedMetadata = new byte[usermetadata.get(index).length];
    usermetadata.set(index, zeroedMetadata);
    byte[] zeroedData = new byte[data.get(index).length];
    data.set(index, zeroedData);
  }
Zeros out user metadata and blob content for the blob indexed at the given {@code index}
@param index the index of the blob that needs to be zeroed out
ambry-server/src/integration-test/java/com/github/ambry/server/ServerHardDeleteTest.java