Bug Report: JMeter Adds Invalid "charset" Parameter to multipart/form-data Content-Type Header

[ThorbenKonopka]

Expected behavior

According to RFC 7578 section 8:
The multipart/form-data media type has no required parameters other than boundary and no optional parameters. However, jmeter adds a charset parameter to the Content-Type header when sending multipart/form-data requests.

The Content-Type header should only contain the boundary parameter:

Content-Type: multipart/form-data; boundary=6WHBdCwuCrCqKt-bDCQyRLPETfeXcy-5twdnz

Actual behavior

The Content-Type header includes an invalid charset parameter:

Content-Type: multipart/form-data; boundary=6WHBdCwuCrCqKt-bDCQyRLPETfeXcy-5twdnz; charset=UTF-8

Steps to reproduce the problem

1. Create an HTTP-Request Sampler
2. Set the method to POST
3. Add a file
4. Check the Use multipart/form-data box
5. Run the request and inspect the headers of that request

JMeter Version

5.6.3

Java Version

No response

OS Version

No response