code: public SharedSet getSharedSet( AbstractJcrNode shareableNode ) {
          NodeKey shareableNodeKey = shareableNode.key();
          return sharedSets.computeIfAbsent(shareableNodeKey, key -> new SharedSet(shareableNode));
      }
docs: Get the {@link SharedSet} for the given shareable node.
  
  @param shareableNode the shareable node
  @return the SharedSet; never null