My machine is still on JVM 11.0.1. Going to have to go through Travis this time around to debug this issue...
Gradle javadoc plugin fails with latest JDK 11 release 
The javadoc plugin fails with a status code 1 on current JVM 11.0.2 releases.
build.gradle
build.gradle
diff --git a/build.gradle b/build.gradle
index a047ced6a9..0dac0c72f3 100644
--- a/build.gradle
+++ b/build.gradle
@@ -59,6 +59,12 @@ allprojects { proj ->
         options.warnings = false
         options.encoding = 'UTF-8'
     }
+    tasks.withType(Javadoc) {
+        options.addStringOption('Xdoclint:none', '-quiet')
+        options.addStringOption('encoding', 'UTF-8')
+        options.addStringOption('charSet', 'UTF-8')
+        options.setSource('8')
+    }
     apply plugin: 'checkstyle'
     checkstyle {
        configFile = rootProject.file('config/checkstyle/checkstyle.xml')
