According to #32826 and #32832 problem description and solution proposal, I introduce 2 static methods ofMulti and ofsingle intoMultiValueMap(LinkedMultiValueMap).
Briefly, It simplifies the conversion of Map to LinkedMultiValueMap, enhancing code simplicity and consistency while maintaining backward compatibility.
Now you can use LinkedMultiValueMap.ofSingle(map) to quickly transfer the normal single value map into a multivalue map which match the FormHttpMessageConverter input requirement.
The toMulti method seems useless because it will not need any work if you build a multivalue mao by default.
These are a bit of my personal thinking and not sure if it is true.
Comment From: snicoll
@gdmrw thanks for the PR but both the issues you've referenced are already assigned to someone so they're working on it. You can share your thoughts on the issue but code change can't be accepted due to the assignment.