Unimplemented Operation on BoardAdminServer.update

[Derek Fields _RightStar_]

I wrote the following script to add "jira-administrators" group as a board administrator. This runs in the ScriptRunner console but fails with a

java.lang.UnsupportedOperationException: Not implemented at com.atlassian.greenhopper.service.rapid.view.BoardAdminAOMapper.update(BoardAdminAOMapper.java:73)

error on the last line - here is the code:

import com.atlassian.jira.component.ComponentAccessor;
import com.atlassian.jira.security.groups.GroupManager;
import com.atlassian.greenhopper.model.rapid.RapidView;;
import com.atlassian.greenhopper.manager.rapidview.RapidViewManager;
import com.atlassian.greenhopper.service.rapid.view.RapidViewService;
import com.atlassian.greenhopper.model.rapid.BoardAdmin;
import com.atlassian.greenhopper.service.rapid.view.BoardAdminService;
import com.atlassian.greenhopper.model.rapid.BoardAdmin.Type;

import com.onresolve.scriptrunner.runner.customisers.PluginModuleCompilationCustomiser
import com.onresolve.scriptrunner.runner.customisers.WithPlugin

@WithPlugin("com.pyxis.greenhopper.jira")
// We need a user to retrieve and update the board. this should probably be a service account
def currentUser = ComponentAccessor.getJiraAuthenticationContext().getLoggedInUser();

// This gets all of the boards available to the current user
// We are going to randomly pick the first one, just for testing purposes
// In a Listener, the event should provide the board and we won't have to look it up
// Note that a Board is called a RapidView
RapidViewService rapidViewService = PluginModuleCompilationCustomiser.getGreenHopperBean(RapidViewService);
List<RapidView> boards = rapidViewService.getRapidViews(currentUser).get();
RapidView ourBoard = boards[0]

// Now we construct a new list of BoardAdmins using the current BoardAdmin list as our base
BoardAdminService boardAdminService = PluginModuleCompilationCustomiser.getGreenHopperBean(BoardAdminService);
List<BoardAdmin> boardAdmins = boardAdminService.getBoardAdmins(ourBoard).collect {it};

// Add the new admin to the boardAdmins list.
// This line constructs a new BoardAdmin
def group = ComponentAccessor.getGroupManager().getGroup("jira-administrators");
BoardAdmin newAdmin = BoardAdmin.builder().key(group.getName()).type(BoardAdmin.Type.GROUP).build();
boardAdmins.add(newAdmin);

// Update the board admins
boardAdminService.updateBoardAdmins(ourBoard, currentUser, boardAdmins);

the last line fails with the error above. 

If I change the last line to 

// Update the board admins
boardAdminService.updateBoardAdmins(ourBoard, currentUser, [newAdmin]);

it works. I don't see any difference between the two versions. Both are java.util.ArrayList classes. Both contain valid BoardAdmin objects. I don't understand why the first one fails and the second one runs. Any ideas are greatly appreciated.