fe26b7d3fd
Prior to this commit, the `NettyHeadersAdapter` would directly delegate
the `add()` and `set()` calls to the adapted
`io.netty.handler.codec.http.HttpHeaders`. This implementation rejects
`null` values with exceptions.
This commit aligns the behavior here with other implementations, by not
rejecting null values but simply ignoring them.
Fixes gh-26277
(cherry-picked from commit 83c19cd60e)