How to pass a group of checkbox values ​​in a form?

Question

Google Apps Script

There is a form with checkboxes, which I pass it through Actions Google Scripts to a Google spreadsheet. If I specify one of several options, then everything works out well - the correct option is entered in the cell, if I select several, then with such a data transfer form['checkbox_name[]']

SpreadsheetApp.openById(SHEET_ID).getSheets()[0].appendRow([new Date(), form['name'], form['phone'], form['email'], form['checkbox_name[]']].concat(res));

I get the following entry in the cell
[Ljava.lang.Object;@556935f1
And with this form['checkbox_name']

SpreadsheetApp.openById(SHEET_ID).getSheets()[0].appendRow([new Date(), form['name'], form['phone'], form['email'], form['checkbox_name']].concat(res));

undefined
The checkbox group itself. What am I doing wrong?

<div class="ss-form-entry">
  <label class="ss-q-title" for="checkbox_name[]">Выберите необходимые виды работ <span class="ss-required-asterisk">*</span></label>
  <ul class="checkbox-group required">
    <li><label><span class="ss-choice-item-control goog-inline-block"><input type="checkbox" name="checkbox_name[]" value="Работа 1" class="ss-q-checkbox"></span>
                    <span class="ss-choice-label">Работа 1</span></label></li>
    <li><label><span class="ss-choice-item-control goog-inline-block"><input type="checkbox" name="checkbox_name[]" value="Работа 2" class="ss-q-checkbox"></span>
                    <span class="ss-choice-label">Работа 2</span></label></li>
    <li><label><span class="ss-choice-item-control goog-inline-block"><input type="checkbox" name="checkbox_name[]" value="Работа 3" class="ss-q-checkbox"></span>
                    <span class="ss-choice-label">Работа 3</span></label></li>
    <li><label><span class="ss-choice-item-control goog-inline-block"><input type="checkbox" name="checkbox_name[]" value="Работа 4" class="ss-q-checkbox"></span>
                    <span class="ss-choice-label">Работа 4</span></label></li>
    <li><label><span class="ss-choice-item-control goog-inline-block"><input type="checkbox" name="checkbox_name[]" value="Работа 5" class="ss-q-checkbox"></span>
                    <span class="ss-choice-label">Работа 5</span></label></li>
  </ul>
</div>

Answer 1

[Ljava.lang.Object;@556935f1is an array. Tables do not support complex types. Try casting the array to a string.
Instead , you can or as a variant of the previous form['checkbox_name[]']

JSON.stringify(form['checkbox_name[]'], null, '  ')