In JIRA we have a single select custom field called 'Severity'. This field is a required field, so will pop-up in the JIRA-Macro when the issue is created from Confluence. We do not have a default value for this field selected:

The behavior in JIRA is that on the create screen this value has by default no value, showing "None". The user has to choose a value. This is exactly the behavior we prefer; forcing the user to think about the value this field should have on creating an issue:

When a user creates an issue from our linked Confluence instance, the field is shown on the create screen, but already has a value assigned. So the user is not forced to select a value in this case:

We would expect to have the same behavior here.