Facet/Advanced Search - "Site" facet not working

When adding a new facet filter for "Site" it does not show up.

To reproduce

• Install 201701GA
• Create 3 sites
• Add the same test document to each site
• Go to the Search admin page and add a new facet for "Site"
• Search for the document

Expected: The document is found 3 times, and the facet filter is shown.
Actual: Document is found 3 times, but facet filter not present.

When looking at the raw JSON
In facets section

		"@{http:\/\/www.alfresco.org\/model\/site\/1.0}site":
		[
		],

it includes the facet filer, but no items in the filter.