[BUG] RestXQ has a failure when returning XML for an HTTP GET in Java 16

[lcahlander]

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Describe the bug
When calling the REST API http://localhost:8080/exist/restxq/error/test from the following application, an HTTP 500 error occurs.

https://github.com/lcahlander/test.git

Expected behavior
An XML document should be returned.

Context (please always complete the following information):

• OS: [e.g. macOS 11.5]
• eXist-db version: [e.g. 5.3.0]
• Java Version [e.g. Java16]

Additional context

• How is eXist-db installed? DMG
• Any custom changes in e.g. conf.xml? None

[duncdrum]

possibly related, I'm getting a lot of 500 on HEAD of develop see eXist-db/dashboard#199