Error while starting game (1.8.9)

Hello.

I am currently trying to make a mod that uses the Firebase Admin SDK as a database backend. I've been having issues getting it to work though, and the closest I've been to is this. My game will start and then crash. I have a feeling it has something to do with the way I'm implementing the Firebase Admin SDK as my game runs perfectly fine without it.

Minecraft error:

java.lang.NoSuchFieldError: JAVA_LETTER_OR_DIGIT
	at net.minecraftforge.common.config.Configuration.<clinit>(Configuration.java:60)
	at net.minecraftforge.common.ForgeModContainer.<init>(ForgeModContainer.java:108)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
	at java.lang.Class.newInstance(Class.java:442)
	at net.minecraftforge.fml.common.Loader.identifyMods(Loader.java:339)
	at net.minecraftforge.fml.common.Loader.loadMods(Loader.java:488)
	at net.minecraftforge.fml.client.FMLClientHandler.beginMinecraftLoading(FMLClientHandler.java:208)
	at net.minecraft.client.Minecraft.startGame(Minecraft.java:451)
	at net.minecraft.client.Minecraft.run(Minecraft.java:360)
	at net.minecraft.client.main.Main.main(Main.java:116)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
	at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at net.minecraftforge.gradle.GradleStartCommon.launch(GradleStartCommon.java:97)
	at GradleStart.main(GradleStart.java:26)

build.gradle: Pastebin

If anybody could help me, that would be greatly appreciated!

Edited September 25, 20196 yr by ShiftedGaming