CSV#build_header_fields_converter

# File tmp/rubies/ruby-3.3.0/lib/csv.rb, line 2804
def build_header_fields_converter
  specific_options = {
    builtin_converters_name: :HeaderConverters,
    accept_nil: true,
  }
  options = @base_fields_converter_options.merge(specific_options)
  build_fields_converter(@initial_header_converters, options)
end