Unable to assign issue with Jira 11

[gnl42]

java.util.concurrent.CompletionException: RestClientException{statusCode=Optional[400], ErrorCollections=[ErrorList [status=400, errorMessages=[], errors={assignee=expected Object containing a 'name' property}]]}
at java.base/java.util.concurrent.CompletableFuture.reportJoin(CompletableFuture.java:413)
at java.base/java.util.concurrent.CompletableFuture.join(CompletableFuture.java:2118)
at me.glindholm.connector.eclipse.internal.jira.core.service.rest.JiraRestClientAdapter.lambda$8(JiraRestClientAdapter.java:725)
at me.glindholm.connector.eclipse.internal.jira.core.service.rest.JiraRestClientAdapter.call(JiraRestClientAdapter.java:734)
at me.glindholm.connector.eclipse.internal.jira.core.service.rest.JiraRestClientAdapter.updateIssue(JiraRestClientAdapter.java:723)
at me.glindholm.connector.eclipse.internal.jira.core.service.JiraClient.updateIssue(JiraClient.java:774)
at me.glindholm.connector.eclipse.internal.jira.core.JiraTaskDataHandler.postTaskData(JiraTaskDataHandler.java:1165)
at org.eclipse.mylyn.internal.tasks.core.sync.SubmitTaskJob.run(SubmitTaskJob.java:103)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:63)
Caused by: RestClientException{statusCode=Optional[400], ErrorCollections=[ErrorList [status=400, errorMessages=[], errors={assignee=expected Object containing a 'name' property}]]}
at me.glindholm.jira.rest.client.internal.async.DelegatingPromise.lambda$0(DelegatingPromise.java:39)
at java.base/java.util.concurrent.CompletableFuture.uniWhenComplete(CompletableFuture.java:863)
at java.base/java.util.concurrent.CompletableFuture$UniWhenComplete.tryFire(CompletableFuture.java:841)
at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:510)
at java.base/java.util.concurrent.CompletableFuture.postFire(CompletableFuture.java:614)
at java.base/java.util.concurrent.CompletableFuture$UniWhenComplete.tryFire(CompletableFuture.java:844)
at java.base/java.util.concurrent.CompletableFuture$Completion.exec(CompletableFuture.java:483)
at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:387)
at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1312)
at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1843)
at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1808)
at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:188)
Caused by: RestClientException{statusCode=Optional[400], ErrorCollections=[ErrorList [status=400, errorMessages=[], errors={assignee=expected Object containing a 'name' property}]]}
at me.glindholm.jira.rest.client.internal.async.AbstractAsynchronousRestClient.lambda$2(AbstractAsynchronousRestClient.java:177)
at java.base/java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:646)
... 9 more