Sandbox module not running with JDK12

Trying to build with JDK12 yields test errors:

• https://travis-ci.org/apache/incubator-tamaya-sandbox/jobs/526972809
• https://travis-ci.org/apache/incubator-tamaya-sandbox/jobs/526972157

{{org.apache.tamaya.management.internal.ManagedConfigTest
[ERROR] testGetTransitiveAreas(org.apache.tamaya.management.internal.ManagedConfigTest) Time elapsed: 0.026 s <<< FAILURE!
org.junit.ComparisonFailure: expected:<[tru]e> but was:<[fals]e>
at org.apache.tamaya.management.internal.ManagedConfigTest.testGetTransitiveAreas(ManagedConfigTest.java:85)
[INFO]
[INFO] Results:
[INFO]
[ERROR] Failures:
[ERROR] ManagedConfigTest.testGetTransitiveAreas:85 expected:<[tru]e> but was:<[fals]e>}}