[Redmine BT] Impossible to report a new issue on Redmine 5.1.1

Affected version : Squash TM 6.0.0.RELEASE & Redmine BT 6.0.0.RELEASE

Steps to reproduce

Try to report a new issue from Squash on Redmine

Expected result

Declaration forms are displayed

Observed behaviour

An error occurs on GUI:
Please find attached the logs error. Error.txt It is still possible to attach an existing issue. Tests made with Postman are passed successfully.

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