code: private AttributeUpdate generateBackpointerRemoval(long fromOffset) {
          return new AttributeUpdate(getBackpointerAttributeKey(fromOffset), AttributeUpdateType.Replace, Attributes.NULL_ATTRIBUTE_VALUE);
      }
docs: Generates an AttributeUpdate that removes a Backpointer, whether it exists or not.
  
  @param fromOffset The offset at which the Backpointer originates.