Unable to proceed massaction "Update attributes" with required multiple select attribute

[tcurilla]

Preconditions

1. Magento ver. 2.2.0
2. PHP 7.0.24

Steps to reproduce

1. clean install
2. create product attribute Multiple Select with id "test_multiselect" and set required values to true
3. fill some options values
4. create product with previously created multiple select attribute
5. save product
6. In Adminhtml -> Catalog -> Products grid select product and do massaction "Update attributes"
7. click on SAVE

Expected result

1. Saving must be processed without error

Actual result

1. Error "The value of attribute "test_multiselect" must be set" is shown
   

Possible solution

In class method \Magento\Framework\Data\Form\Element\Multiselect::getElementHtml()
add "id" attribute to hidden element

if ($this->getCanBeEmpty()) {
    $html .= '<input type="hidden" name="' . parent::getName() . '" value="" />';
}

change to

if ($this->getCanBeEmpty()) {
    $html .= '<input type="hidden" id="' . $this->getHtmlId() . '_hidden" name="' . parent::getName() . '" value="" />';
}

see Magento_Catalog view/adminhtml/web/catalog/product.js disableFieldEditMode/enableFieldEditMode methods

[magento-engcom-team]

@tcurilla, thank you for your report.
We've created internal ticket(s) MAGETWO-81398 to track progress on the issue.