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My mod won't start 1.16.1, (Exception in thread "main" java.lang.NoClassDefFoundError, Caused by: java.lang.ClassNotFoundException)


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Hi I'm currently working on a mod that adds variants of blocks into MC. 

My version is 1.16.1 and I'm using Intellij to write my code. Here's the exception:


Exception in thread "main" java.lang.NoClassDefFoundError: cpw/mods/modlauncher/Launcher
    at net.minecraftforge.userdev.LaunchTesting.main(LaunchTesting.java:105)
Caused by: java.lang.ClassNotFoundException: cpw.mods.modlauncher.Launcher
    at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:352)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
    ... 1 more


It only appears in my debug log when I debug-run the runClient configuration, as I cannot find anything in my crash reports folder. There isn't any additional information on it.

It's my first mod, so am I doing something wrong?

I've already added about 50 blocks, they all work in game, and I've never encountered a crash like this one before. How should I fix it?

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