You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: workflow_step.rb
    path of file: ./repos/acidic_job/lib/acidic_job
    
    the code of the file until where you have to start completion: # frozen_string_liter
    
    def iterable_key
      # the `iterable_key` represents the name of the collection accessor
      # that must be present in `@run.attr_accessors`; that is,
      # it must have been passed to `persisting` when calling `with_acidic_workflow`
      for_each = @run.current_step_hash["for_each"]

      return unless for_each.present?

      return for_each if @run.attr_accessors.key?(for_each)

      raise UnknownForEachCollection
    end