klass = Struct.new(:runner_type, :output_type, keyword_init: true)
# correct output
puts klass.new({}) # -> #<struct runner_type=nil, output_type=nil>

klass.prepend(Module.new {
       def initialize(**options)
          puts options.inspect
          super(options)
        end
      })

# wrong output -> runner_type is initialized to {}
puts klass.new({}) # -> #<struct runner_type={}, output_type=nil>