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.