Multiple new lines not accepted in description

Summary

When using the new releases API, a new-line character (0xa) causes the API to respond with a HTTP/1.1 400 Bad Request error.

Steps to reproduce

I bumped into this while trying to publish a release from .gitlab-ci.yml

script:
    - CI_COMMIT_TAG_MESSAGE="$(printf "A\n\nB\n)"
    - echo "${CI_COMMIT_TAG_MESSAGE}" | hexdump -C
    - |
      curl \
        --data "{\"tag_name\": \"${CI_COMMIT_TAG}\", \"name\": \"${CI_PROJECT_NAME} ${CI_COMMIT_TAG}\", \"description\": \"${CI_COMMIT_TAG_MESSAGE:-No release notes.}\"}" \
        --fail \
        --header "Content-Type: application/json" \
        --header "Private-Token: ${CI_PRIVATE_TOKEN}" \
        --output "/dev/null" \
        --request POST \
        --show-error \
        --silent \
        --trace-ascii "/dev/stderr" \
        --write-out "HTTP response: %{http_code}\n\n" \
        "${CI_API_V4_URL}/projects/${CI_PROJECT_ID}/releases"

is the exact step I performed. It is quite easy to do this locally with cURL of course (I did, but without the hexdump echoing to validate the output)

While markdown seems to work, new-lines do not.

What is the current bug behavior?

$ echo "${CI_COMMIT_TAG_MESSAGE}" | hexdump -C
00000000  41 0a 0a 42 0a                                    |A..B.|
00000005
$ curl \ # collapsed multi-line command
<snip>
=> Send data, 87 bytes (0x57)
0000: {"tag_name": "v1", "name": "v1",
0040:  "description": "A..B"}
== Info: upload completely sent off: 87 out of 87 bytes
<= Recv SSL data, 5 bytes (0x5)
0000: ....k
== Info: The requested URL returned error: 400 Bad Request

Further more; a standard line (with one new line at the end) does work normally.

What is the expected correct behavior?

201 Request accepted

Output of checks

This bug happens on GitLab.com