How to javadoc 9+ many independent projects into a single output

I’m trying to crate a single javadoc output for a set of independent library projects.

Prior to javadoc 9+ I could do so by just collecting previously generated source jars from a special dependency set like so:
dependencies {
javadocs myGroup:myLibProject:myVersion:sources
task allJavaDocs(type: Javadoc) {
source configurations.javadocs.collect { zipTree(it) }
include ‘**/*.java’

The resulting fileset does only contain my “own” files, so a lot of references to for instance Annotations or constants from external jars are missing. Which I don’t mind!

With javadoc 8 this was not a problem, as the option -Xdoclint:none ignores missing references. I got what I wanted: my own library stuff documented in a single place.

javadoc 9+ seems to work differently though. It throws errors regarding missing references and refuses to go on and just document what has been provided.

I’m currently stuck.

I’d like to have a combined javadoc of multiple independent projects while just ignoring or not documenting stuff that’s missing.