Github release failed because of POST request

[TimvdLippe]

https://travis-ci.org/mockito/mockito/jobs/542208671#L2027

[performRelease] > Task :updateReleaseNotesOnGitHub FAILED
[performRelease]   Building new release notes based on /home/travis/build/mockito/mockito/doc/release-notes/official.md
[performRelease] POST /repos/mockito/mockito/releases
[performRelease] 
[performRelease] > Task :junit-jupiter:bintrayUpload
[performRelease] Uploaded to 'https://api.bintray.com/content/mockito/maven/mockito-development/3.0.0/org/mockito/mockito-junit-jupiter/3.0.0/mockito-junit-jupiter-3.0.0.pom'.
[performRelease] 
[performRelease] > Task :bintrayPublish
[performRelease] 
[performRelease] 
[performRelease] FAILURE: Build failed with an exception.
[performRelease] Deprecated Gradle features were used in this build, making it incompatible with Gradle 6.0.
[performRelease] 
[performRelease] Use '--warning-mode all' to show the individual deprecation warnings.
[performRelease] * What went wrong:
[performRelease] See https://docs.gradle.org/5.3.1/userguide/command_line_interface.html#sec:command_line_warnings
[performRelease] Execution failed for task ':updateReleaseNotesOnGitHub'.
[performRelease] 92 actionable tasks: 36 executed, 56 up-to-date
[performRelease] > java.io.IOException: POST https://api.github.com/repos/mockito/mockito/releases failed, response code = 400, response body:
[performRelease]   {"message":"Problems parsing JSON","documentation_url":"https://developer.github.com/v3/repos/releases/#create-a-release"}

I am not sure what the exact cause is, as the stacktrace does not mention the actual root cause exception.