bug: Flow with empty input does not accept empty input

[wasnertobias]

Describe the bug

Created a newly flow for #3701 and was surprised that I cannot POST an empty body. It does return the following (not trigger the flow):
Bad request: invalid json: EOF while parsing a value at line 1 column 0

Workaround was to simply put "{}" in the body.

To reproduce

Create a new flow and try to call it from webhook without any payload.

Expected behavior

Empty payload is accepted if the flow input is empty.

Screenshots

No response

Browser information

Chrome Version 124.0.6367.119

Application version

EE v1.323.6-12-gee2a19395

Additional Context

No response