Caused by: java.io.FileNotFoundException: whatever_mod:models/item/tutorial_item.json

This results in the item having no texture at all. The same thing happens in an normal Java project. It has something to do with IntelliJ Idea. The workaround in a Java project is to at at the bottom of the "build.gradle" file sourceSets { main { output.resourcesDir = output.classesDir } }. This workaround does not work with Forgelin! The only way I could get it to run was by running it via gradlew runClient. But this is a very slow and bad solution.

I am using Alex Couch tutorial mod (after updating gradle to 4.9, changing the project kotlin version to my version ext.kotlin_version = '1.3.61' and adding apply plugin: 'kotlin' to build.gradle) and IntelliJ Idea Ultimate 2019.3!

https://forums.minecraftforge.net/topic/77064-solved-modding-with-intellij-the-asset-problem/?tab=comments#comment-370253

Also happening with java/scala. But still does not fix it

I've also been having this problem and haven't been able to find a working solution, at least in Kotlin. It looks like the IntelliJ fix seems(?) to work if I'm using Java. I have had to do sourceSets { main { output.resourcesDir = output.classesDir } } with Java.