Issues not accessible via REST if Priority field is null

What happen is the following:

• by using the Default Field Configuration the Priority field show up on the screen by default
• when you create a new issue, even then the Priority field is not mandatory, you need to pick up a value or the default will be set (there is no possibility to set a null value)
• if you Hide the Priority field, you are able to create an issue with a null Priority value and then the REST link (http://localhos:8080/rest/api/2.0.alpha1/issue/AAA-1) will work
• but if you Show the Priority field after the issue is already created, the value for Priority in the db will be null and you will not be able to access the issue trough the REST link. It will show the following:

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<status>
<status-code>404</status-code>
</status>