Customer errors with an argument

custom_errors.rb

# Custom errors with arguments
#
# Example usage:
#
#   ENV.fetch('BLAH') { raise EnvironmentError.new('BLAH') }
class EnvironmentError < StandardError
  attr_reader :key

  def initialize(key)
    @key = key
  end

  def message
    "A required ENV key, #{key}, is missing. Check the README"
  end
end

A good example here via here