Weird "cannot convert xs:boolean('true') to a node set" message

[xatapult]

trafficstars

What is the problem`

The following XQuery gives an error message that as far as I understand things doesn't make sense:

let $col as document-node()* := collection('/db/apps/dashboard')
let $doc as element()* := $col/xyz (: Resolves to an empty sequence :)
return 
  $doc/*[not(self::abc)]
  (: Results in: exerr:ERROR cannot convert xs:boolean('true') to a node set :)

What did you expect

An empty sequence as output

Describe how to reproduce or add a test

Run the XQuery above

Context information

Please always add the following information

• eXist 4.3.1 build 201807241821
• Java version 1.8.0_181
• Operating system W10
• 64 bit
• JAR installed
• Any custom changes in e.g. conf.xml? Data directory moved to outside eXist installation directory