configureExchangesAndQueues does not check for a null profile

[JAertgeerts]

If the process is no worker, the application shuts down as
TypeError: Cannot read property 'tasks' of undefined

This because profile can be null, as stated in the method configuration (if the process is not a worker). The configure method will fail because you're accessing the profile object in the configureExchangesAndQueues method.

/**
  * configure rabbitmq exchanges, queues, bindings and handlers
  */
 configure() {
   let taskerConfig = this.app.config.tasker
   const profile = getWorkerProfile(taskerConfig)
   taskerConfig = configureExchangesAndQueues(profile, taskerConfig)

   this.app.tasker = new Client(this.app, rabbit, taskerConfig.exchangeName)
   TaskerUtils.registerTasks(profile, this.app, rabbit)

 }

I can open a PR to check if profile is null or do you want to handle it differently?
My current solution is just the following:

 /**
 * configure rabbitmq exchanges, queues, bindings and handlers
 */
configure() {
  let taskerConfig = this.app.config.tasker
  const profile = getWorkerProfile(taskerConfig)
  if (profile) {
    taskerConfig = configureExchangesAndQueues(profile, taskerConfig)

    this.app.tasker = new Client(this.app, rabbit, taskerConfig.exchangeName)
    TaskerUtils.registerTasks(profile, this.app, rabbit)
  }
}