updated comment so the behaviour is clearer when looking at swagger UI.

#1970

j-lawyer-server/j-lawyer-io/src/java/org/jlawyer/io/rest/v7/CasesEndpointV7.java

@@ -968,7 +968,7 @@ public Response getDocumentsByTag(@PathParam("tag") String tag) {
     }
 
     /**
-     * Updates a cases allowed groups. All allowed groups must be submitted in one request - existing permissions will be overwritten, not added to. This endpoint can also be used to reset security for a case by sending an empty list of groups.
+     * Updates a cases allowed groups. All allowed groups must be submitted in one request - existing permissions will be overwritten, not added to. This endpoint can also be used to reset security for a case by sending an empty list of groups. Providing the ID of a group is sufficient.
      *
      * @param id case ID
      * @param allowedGroups the groups allowed to access the case