The checkJvmVersion() function in the /bin/inc script of the distribution is not dealing with the new output of java -version of JDK10 (and later?).
The VERSION variable is left undefined, which then has the main bootscript to not set the Jigsaw modules correctly (the various JVM flags which need to be enabled since Java 9).
This is a blocker to use Karaf on Java 10, which is already in candidate release. I don't think much else is changed compared to Java 9 so it would be great to sort this.