magento2: Unable to unselect all multiselect values

This issue still persist in Magento ver. 2.2.2

Still this issue also persist at magento 2.2.4 .

Have done with Vinai describe scenario and same issue is happening

@Vinai ,Is this issue resolved at your end?

@magento/community-engineering-team ,Can you please check this issue again

I had the same issue because of multiselect having an empty value (ie. equal to ‘’ or 0 or null) :

<select multiple="" class="admin__control-multiselect" data-bind="
    attr: {
        name: inputName,
        id: uid,
        size: size ? size : '6',
        disabled: disabled,
        'aria-describedby': noticeId,
        placeholder: placeholder
    },
    hasFocus: focused,
    optgroup: options,
    selectedOptions: value,
    optionsValue: 'value',
    optionsText: 'label'" name="product[customer_group]" id="MEAKNUP" size="6" aria-describedby="notice-MEAKNUP">
   <option data-title="NOT LOGGED IN" value="0">NOT LOGGED IN</option> <!-- here is the devil -->
   <option data-title="General" value="1">General</option>
   <option data-title="Conseillère" value="2">Conseillère</option>
</select>

Magento\Catalog\Controller\Adminhtml\Product\Initialization\Helper\AttributeFilter prepare your attributes before saving it.

public function prepareProductAttributes(Product $product, array $productData, array $useDefaults)
{
    foreach ($productData as $attribute => $value) {
        $considerUseDefaultsAttribute = !isset($useDefaults[$attribute]) || $useDefaults[$attribute] === "1";
        if ($value === '' && $considerUseDefaultsAttribute) {
            /** @var $product Product */
            if ((bool)$product->getData($attribute) === (bool)$value) {
                unset($productData[$attribute]);
            }
        }
    }
    return $productData;
}

When a posted value is equal to empty string (‘’) it will compare it to the product value before saving. The issue is that Magento cast both values in boolean. And when the previously selected product value was set to 0 (like “NOT LOGGED IN” in our example) it compares an empty string casted in boolean (= false) with a 0 casted in boolean (= false too) so the value is simply unset … so the attribute isn’t saved and there is no error.

In our specific case, we fixed it using a plugin to restore the value after the prepareProductAttributes function has been called.

I hope it will help.

Still present in Magento ver. 2.2.3

I’d like to know how to get this fixed. It’s driving me nuts. (Tested on both 2.1.2 and 2.1.6)