In GrouperServiceLogic.java membershipIds are always set to null.

See master branch lines 1737 & 1757. Removing both lines should do the trick, as the membershipids are set in 1738 - 1742.

Example WS request:

http://localhost:8080/grouper-ws/servicesRest/v2_2_000/memberships
{
"WsRestGetMembershipsRequest":

{ "includeGroupDetail": "T", "membershipIds": ["...."], "includeSubjectDetail": "T" }

}