Jacoco test report is empty

Use case: code coverage for android library.
See: **https://github.com/heershingenmosiken/android-assertions** repository, branch **jacoco-android** gradle module **android-assertions**.

Tests runs well. There are test report.
Jacoco runs well, but inside it shows that coverage is empty !

See report: https://codecov.io/gh/heershingenmosiken/android-assertions/branch/jacoco-android
See tests passed: https://travis-ci.com/heershingenmosiken/android-assertions/builds/96632553

Actual result: Jacoco report with no coverage inside.
Expected result: Jacoco report with code coverage inside.

Hot to test:
1. Checkout https://github.com/heershingenmosiken/android-assertions/tree/jacoco-android (branch is important)
2. ./gradlew :libAndroidAssertions:jacocoTestReport
3. Check test report and jacoco report.