It is not possible to sort the issues by Epic Link.Key

Description

It is not possible to sort the issues by Epic Link.Key

How to reproduce

1. Use this code:

&{for issues|filter=%{'${IssueTypeName}'.equals('Story')}|sortby=Epic Link.Key}

Epic: ${Epic Link.Key} - ${Epic Link.Summary}

#{end}

Actual result/Attachments
The code breaks the template and the document exported shows the code itself.

Expected result
It should be possible to sort the issues by the epic link key.