Ratpack-hystrix collapser throwing UnmanagedThreadException

CollapserTest.groovy

class CollapserTest extends BaseHttpClientSpec {

    def setup() {
        RxRatpack.initialize()
    }

    def 'exception on collapser command creation'() {
        given:
        otherApp {
            get("foo/:id") { render pathTokens.get("id") }
        }

        and:
        bindings {
            module new HystrixModule()
            bind(CommandFactory)
        }

        handlers { CommandFactory factory ->
            path("collapser") {
                def firstCall = factory.batchCommand().queue()
                Blocking.get {
                    firstCall.get()
                } then {
                    render it
                }
            }

        }

        expect:
        getText(executionType) == "1"

        where:
        executionType << ["collapser"]

    }

    static class CommandFactory {

        private final HttpClient httpClient

        @Inject
        CommandFactory(HttpClient httpClient) {
            this.httpClient = httpClient
        }


        HystrixCollapser<String, String, String> batchCommand() {
            new HystrixCollapser<String, String, String>(
                    HystrixCollapser.Setter.withCollapserKey(
                            HystrixCollapserKey.Factory.asKey("hystrix-collapser"))
                            .andScope(HystrixCollapser.Scope.GLOBAL)) {

                @Override
                String getRequestArgument() {
                    return "hystrix-command-argument"
                }

                @Override
                protected HystrixCommand<String> createCommand(Collection<HystrixCollapser.CollapsedRequest<String, String>> collapsedRequests) {
                    return hystrixCommand('1')
                }

                @Override
                protected void mapResponseToRequests(String batchResponse, Collection<HystrixCollapser.CollapsedRequest<String, String>> collapsedRequests) {
                    // Single response for all requests
                    for (HystrixCollapser.CollapsedRequest<TrackerResult, Event> request : collapsedRequests) {
                        request.setResponse(batchResponse)
                    }
                }
            }
        }

        HystrixCommand<String> hystrixCommand(final String requestNumber) {
            new HystrixCommand<String>(HystrixCommandGroupKey.Factory.asKey("hystrix-command")) {

                @Override
                protected String run() throws Exception {
                    assert Thread.currentThread().name.startsWith("hystrix-${getCacheKey()}-")
                    requestNumber
                }

                @Override
                protected String getCacheKey() {
                    return "hystrix-command"
                }
            }
        }

    }
}