Asset folder not found when running jar - scala

Question

I'm trying to run a jar which accesses a save file from a predefined directory. It runs properly when running with IntelliJ, but When I run it with "java -jar", I get a NullPointerException pointing to the third line in the following snippet:
val dir = new File("./statFiles")
dir.listFiles
.filter(_.getName.takeRight(3) == "cmf")
.map(_.getName)
I get the same exception from IntelliJ if I remove the directory, so it's probably caused by the directory not being found. I'm assuming IntelliJ does something automatically that I should do manually, but I can't tell what the issue is.
edit: I've tried running the jar both from a folder that also houses the 'statFiles' folder as well as from the path in which IntelliJ creates the jar ({project root}/classes/artifacts/{name}_jar).
Stacktrace:
Exception in thread "main" java.lang.ExceptionInInitializerError
at cmsoft.ui.GUI.main(GUI.scala)
Caused by: java.lang.NullPointerException
at scala.collection.ArrayOps$.filter$extension(ArrayOps.scala:191)
at cmsoft.io.FileHandler$.findSavedStats(FileHandler.scala:24)
at cmsoft.io.FileHandler$.findSavedStat(FileHandler.scala:32)
at cmsoft.Control$.startup(Control.scala:30)
at cmsoft.ui.GUI$.<clinit>(GUI.scala:340)
... 1 more