I am trying to set the start node for a MultiNode TreePicker using XSLT.

I have a blog landing page (alias = 'BlogLandingPage') with a property (alias = 'blogCategoryFolder') using the content picker to define a folder containing nodes used to define the blog categories that can be picked.

I want the MultiNode TreePicker to start at the category folder that has been selected on the BlogLandingPage using the content picker.

My XSLT is:

$current/ancestor-or-self::BlogLandingPage/blogCategoryFolder

My blog posts use the MultiNode TreePicker to select the categories available. When I access a blog post in the content tree I get the following error:

failed to retrieve entity data for query $current/ancestor-or-self::BlogLandingPage/blogCategoryFolder

Object reference not set to an instance of an object.

I would expect the XSLT I have used to return the id of the blog category folder.

Is my XSLT wrong or is it just the case that start node of the MultiNode TreePicker cannot be defined in this way?