Grails 3.2.2 Highlighs feature doesn't work

[bioform]

If I use the following example from the documentation

def results = Tweet.search("${params.query}", [highlight: { field 'message' }])

the results.highlight is ArrayList where each element is empty HashMap.
If I will replace 'message' field name to '_all' - I will get the same result - not empty array list with empty HashMap elements.