public Optional<Allocation> getParent() {
    return Optional.ofNullable(parent);
  }
Gets the parent allocation, or {@link Optional#empty} if this is a root allocation. This
allocation represents 1 allocation unit of the parent allocation.

@return the parent {@link Allocation}
jib-core/src/main/java/com/google/cloud/tools/jib/event/progress/Allocation.java