Invalid argument supplied for foreach thrown in EAV code

[wojtekn]

Preconditions

1. Latest Magento 2.3

I spot the problem in M2 Commerce in RMA module, but as problem comes from M2 Open Source core and is clearly visible by code review, I'm adding it here.

Steps to reproduce

1. Enable RMA feature in backend
2. Place order in frontend
3. Invoice and ship order in backend
4. Navigate to order details in My Account pages in frontend
5. Open order details
6. Click "Return"

Expected result

RMA form is displayed

Actual result

Exception is thrown:

1 exception(s):
Exception #0 (Exception): Warning: Invalid argument supplied for foreach() in vendor/magento/module-rma/Block/Returns/Create.php on line 155

The problem looks as introduced in \Magento\Eav\Model\Form::getAttributes where not all class variables are initialized as array, but they are returned by method which suppose to return array:

public function getSystemAttributes()
{
    if ($this->_systemAttributes === null) {
        // load attributes
        $this->getAttributes();
    }
    return $this->_systemAttributes;
}

getAttributes method initializes _attributes and _userAttributes variables as arrays but not _systemAttributes and _allowedAttributes.

I will submit PR for this soon.

[magento-engcom-team]

Hi @wojtekn. Thank you for your report.
To help us process this issue please make sure that you provided the following information:

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• Information on your environment
• Steps to reproduce
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Please make sure that the issue is reproducible on the vanilla Magento instance following Steps to reproduce. To deploy vanilla Magento instance on our environment, please, add a comment to the issue:

@magento-engcom-team give me 2.3-develop instance - upcoming 2.3.x release

For more details, please, review the Magento Contributor Assistant documentation.

@wojtekn do you confirm that you was able to reproduce the issue on vanilla Magento instance following steps to reproduce?

• yes
• no

[magento-engcom-team]

Hi @engcom-backlog-nazar. Thank you for working on this issue.
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[riconeitzel]

@magento-engcom-team give me 2.3-develop instance

[magento-engcom-team]

Hi @riconeitzel. Thank you for your request. I'm working on Magento 2.3-develop instance for you

[magento-engcom-team]

Hi @riconeitzel, here is your Magento instance.
Admin access: https://i-21134-2-3-develop.instances.magento-community.engineering/admin
Login: admin Password: 123123q
Instance will be terminated in up to 3 hours.

[magento-engcom-team]

✅ Confirmed by @engcom-backlog-nazar
Thank you for verifying the issue. Based on the provided information internal tickets MAGETWO-98212, MAGETWO-98213 were created

Issue Available: @engcom-backlog-nazar, You will be automatically unassigned. Contributors/Maintainers can claim this issue to continue. To reclaim and continue work, reassign the ticket to yourself.