build_header_fields_converter

# File lib/csv.rb, line 1393
  def build_header_fields_converter
    specific_options = {
      builtin_converters: HeaderConverters,
      accept_nil: true,
    }
    options = @base_fields_converter_options.merge(specific_options)
    build_fields_converter(@initial_header_converters, options)
  end