src/vs/workbench/contrib/tasks/browser/taskService.ts/TaskService/getTaskSystem
class TaskService:	protected getTaskSystem(): ITaskSystem {
		if (this._taskSystem) {
			return this._taskSystem;
		}
		if (this.executionEngine === ExecutionEngine.Terminal) {
			this._taskSystem = this.createTerminalTaskSystem();
		} else {
			throw new Error(TaskService.ProcessTaskSystemSupportMessage);
		}
		this._taskSystemListener = this._taskSystem!.onDidStateChange((event) => {
			if (this._taskSystem) {
				this._taskRunningState.set(this._taskSystem.isActiveSync());
			}
			this._onDidStateChange.fire(event);
		});
		return this._taskSystem!;
	}