how to Flatten json null to empty string in golang

I am searching for go library or work around to flatten the null json value to empty string (""),
from

`{
	"foo": {
			"jim":null
	}
}`  

to

map[foo.jim:""]  

as of now its being ignored for my use case.
can anybody help me with this.

example code https://go.dev/play/p/9hnMEa6QA2O
you can see that i get the output

map[fee:bar]  

but i want

map[foo.jim:"" fee:bar]

after going through the code,
had to check for nil instead of ignoring it in switch case.

default:
		if v == nil {
			flatMap[newKey] = ""
		} else {
            flatMap[newKey] = fmt.Sprintf("%v", v)
        }