group_by next unless key.present?

lib/tallty_import_export/export.rb

@@ -40,11 +40,13 @@ module TalltyImportExport
         if @group_by.present?
           if records.is_a?(Array)
             records.group_by { |record| record.send(@group_by)}.each do |key, group_records|
+              next unless key.present?
               @group_key = key
               export_workbook workbook, group_records
             end
           else
             records.group(@group_by).count.keys.each do |key|
+              next unless key.present?
               @group_key = key
               export_workbook workbook, records.ransack("#{@group_where}" => key).result
             end