activiti - 返回任务列表

Question

我想返回一个任务列表：

  List<Task> tasks = runtimeService.createProcessInstanceQuery()
            .processDefinitionKeys(workflowKey).list().stream()
            .map(x -> processEngine.getTaskService().createTaskQuery()
                    .includeProcessVariables()
                    .includeTaskLocalVariables()
                            .processInstanceId(x.getProcessInstanceId())
                                    .list())
            .collect(Collectors.toList());

但我有这个错误：

no instance(s) of type variable(s) exist so that List<Task> conforms to Task inference variable T has incompatible bounds: equality constraints: Task lower bounds: List<Task>

：

Required type:
List
<Task>
Provided:
List
<List<Task>>