def validate_headers(row)
      valid_headers = @config.fields - @config.export_only_fields
      #valid_headers += @config.has_ones.map

      row.headers.compact.map(&:to_sym).each do |h|
        unless valid_headers.include?(h)
          logger.warn "ignoring unknown column #{h}"
        end
      end
    end
def validate_headers(row)
      valid_headers = @config.fields - @config.export_only_fields
      #valid_headers += @config.has_ones.map

      row.headers.compact.map(&:to_sym).each do |h|
        unless valid_headers.include?(h)
          logger.warn "ignoring unknown column #{h}"
        end
      end
    end
TODO: don't warn on has_one headers and clean up clunky loop