old-zsterminator/app/serializers/reservation_serializer.rb

class ReservationSerializer < ActiveModel::Serializer
  attributes :id, :start_time, :end_time, :customer_color_emoji
  
  belongs_to :customer
  belongs_to :team, serializer: TeamSerializer

  def customer_color_emoji
    object.customer&.color_emoji || ''
  end
end