bintrayUpload fails when testing shipkit-bootstrap

[mockitoguy]

When following steps from https://github.com/mockito/shipkit-bootstrap project I bumped into following issue:

> Task :bintrayUpload
:bintrayUpload - publishing to Bintray
  - dry run: false, version: 0.0.1, Maven Central sync: true
  - user/org: shipkit-bootstrap-bot/shipkit-bootstrap, repository/package: null/maven


FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':bintrayUpload'.
> java.lang.NullPointerException (no error message)

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.

* Get more help at https://help.gradle.org

BUILD FAILED in 7s