Installing nb-javac library leads to an exception

I have downloaded and installed
Apache NetBeans IDE Dev (Build incubator-netbeans-release-365-on-20181105) (10-vc3).

I got a notification to install the nb-javac library. This leads to an exception (added at the end of the text).

Maybe there was a little java version confusion:

I started NetBeans with configuring jdk1.8.0_191 in netbeans.conf. Some functions like "navigate -> go to declaration did not work" and code completation did not work. Therefore I decided to switch to java 10 and restarted NetBeans. Code complemtation and navigate worked. The notifaction appeared after working with the IDE for some time.

Additionally I have configured a 8.2 update center.