".value" in text modules for external data sources breaks ticket zoom

[Gerrit]

Used Zammad Version

6.3

Environment

• Installation method: SaaS
• Browser + version: Edge Version 123.0.2420.81

Actual behaviour

When using a variable of an external data source ticket attribute in a text module and want to display the label using .value, no ticket with an empty attribute cannot be displayed.

Expected behaviour

I am able to open tickets with empty external data source ticket attributes, even though the text module is configured.

Steps to reproduce the behaviour

Create a ticket attribute with an external data source.
Create a ticket by e-mail (so the attribute is empty).
Create a text module with #{ticket.my_external_data_source.value}.
Try to open the ticket zoom for that ticket.

Support Ticket

Ticket#10152467

I'm sure this is a bug and no feature request or a general question.

yes