Customer group CUST_GROUP_ALL not selected in adminhtml after attribute save

[mashb1t]

Preconditions

1. Magento 2.1.7 EE
2. PHP 7.0.20

Steps to reproduce

1. Call method \Magento\Customer\Model\Customer\Source\Group::toOptionArray

Expected result

1. All $customerGroups['value'] should be of type string

Actual result

1. First customer group value (\Magento\Customer\Api\Data\GroupInterface::CUST_GROUP_ALL) is integer

Solution

1. Cast GroupInterface::CUST_GROUP_ALL to string

magento2/app/code/Magento/Customer/Model/Customer/Source/Group.php

Line 59 in 354fc11

'value' => GroupInterface::CUST_GROUP_ALL,

When using the result of \Magento\Customer\Model\Customer\Source\Group::toOptionArray as options in an (multiselect) attribute source model, the respective customer group CUST_GROUP_ALL is not getting selected in the Magento Admin-Panel despite the value of the group being set.

[magento-team]

Internal ticket to track issue progress: MAGETWO-71432