intellij plugin SDK can't resolve java

my plugin project can't find any java classes. How can I make my project compile again? I'm developing on manjaro

project: https://github.com/axaluss/power-mode-intellij-plugin

DISTRIB_ID=ManjaroLinux
DISTRIB_RELEASE=18.1.2
DISTRIB_CODENAME=Juhraya
DISTRIB_DESCRIPTION="Manjaro Linux"

IntelliJ IDEA 2019.2.4 (Community Edition)
Build #IC-192.7142.36, built on October 29, 2019
Runtime version: 11.0.4+10-b304.77 amd64
VM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
Linux 5.2.21-1-MANJARO
GC: ParNew, ConcurrentMarkSweep
Memory: 1948M
Cores: 6
Registry: 
Non-Bundled Plugins: Batch Scripts Support, CMD Support, dcevm, de.ax.powermode, mobi.hsz.idea.gitignore, net.seesharpsoft.intellij.plugins.csv, org.intellij.scala, BashSupport, org.toml.lang, some.awesome

Solution

I figured it out. Somehow the "project sdk" was broken. I set it up freshly while I was figuring it out. But somehow deleting it and creating it a second time fixed it.