ForeignSourceConfigRestService is the handler responsible for /opennms/rest/foreignSourcesConfig
That is the ReST end-point to obtain the available policies, detectors, categories, assets and services.
After the addition of the WS-MAN feature (specifically a detector), retrieving the detectors through ReST stopped working and throws a NPE.
If I remove the JARs for WS-MAN and restart OpenNMS, I can retrieve the detectors as usual without issues.
I figured out that when calling org.opennms.netmgt.provision.persist.ForeignSourceService.getDetectorTypes(), which is supposed to return a Map<String,String>, the key for the WS-MAN detector is not a string:
The expected information on that map, for a detector looks like this: