Unable to run client because java lang NullPointerException or something

Caused by: net.minecraftforge.fml.ModLoadingException: Tutorial Mod has class loading errors

Caused by: java.lang.NullPointerException: Cannot invoke "java.lang.Class.getName()" because "this.modClass" is null

This question has nothing to do with Gradle, besides that you maybe you Gradle to build your software, and thus is offtopic here.
Please find a more appropriate forum or community to ask your question in.