JSON conversion fails after fetch with template literal

[PHvL]

Hi,
I'm trying to update to v0.9.91.

If we use template literals in fetch, a conversion to JSON fails:

fetch `/api?${#form as Values | FormEncoded}` as JSON

fails with "Uncaught SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data"
Same for

set params to 'study_id=163017051' fetch `/api?${params}` as JSON

explicitely putting the form data as string

fetch /api?study_id=163017051 as JSON

works.

Since

fetch `/api?${#form as Values | FormEncoded}` as Text

fails with "Uncaught Error: Unknown conversion : Text", my suspicion is, that the internal output of #form as Values | FormEncoded is fed to the external conversion.

Am I doing something wrong?

Best regards
Philipp