I started with jdk and had the same issue. I tried Oracle to see if there was an issue with jdk in Mint w/ the launcher.
from my brief search that error "java.lang.reflect.InaccessibleObjectException: Unable to make public void jdk.internal.ref.Cleaner.clean" seems to be specific to v9, (and later.)
linky
As far as my limited understanding goes it shouldn't happen in v8 as it's caused by a change made in v9.
To add to that, in my experience the openjjdk in nix is a lot more reliable and far easier to use due to it being in your repo, specifically built for your distro and only an apt away. Do an apt remove --purge on Oracle and try again with openjdk-8.
(I'm not even sure StarMade works with java above v8? Anyone?)