public ScheduleOptions whenExistsDoNothing() {
      this.whenExists = WhenExists.DO_NOTHING;
      return this;
    }
Gets the details for a specific scheduled execution. Currently running executions are also
returned.

@param taskInstanceId
@return Optional.empty() if no matching execution found
@see com.github.kagkarlsson.scheduler.task.TaskInstanceId
@see com.github.kagkarlsson.scheduler.ScheduledExecution
db-scheduler/src/main/java/com/github/kagkarlsson/scheduler/SchedulerClient.java