class ActiveSupport::Callbacks::Callback

def merge_conditional_options(chain, if_option:, unless_option:)
  options = {
    if: @if.dup,
    unless: @unless.dup
  }
  options[:if].concat     Array(unless_option)
  options[:unless].concat Array(if_option)
  self.class.build chain, @filter, @kind, options
end