code: function assignExtraMetrics(ctx, name, payload) {
  	let def = ctx.action.metrics[name];
  	// if metrics definitions is boolean do default, metrics=true
  	if (def === true) {
  		payload[name] = ctx[name];
  	} else if (_.isArray(def)) {
  		payload[name] = _.pick(ctx[name], def);
  	} else if (_.isFunction(def)) {
  		payload[name] = def(ctx[name]);
  	}
  }
docs: Assign extra metrics taking into account action definitions
  
  @param {Context} ctx
  @param {string} name Field of the context to be assigned.
  @param {any} payload Object for assignment.
  
  @private