Tell me what I did wrong.

So I have an item using what forge says as the code, and I try to launch, and heres what the console says:

[12:45:02] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLTweaker
[12:45:02] [main/INFO] [LaunchWrapper]: Using primary tweak class name cpw.mods.fml.common.launcher.FMLTweaker
[12:45:02] [main/INFO] [LaunchWrapper]: Calling tweak class cpw.mods.fml.common.launcher.FMLTweaker
[12:45:02] [main/INFO] [FML]: Forge Mod Loader version 7.2.217.1147 for Minecraft 1.7.2 loading
[12:45:02] [main/INFO] [FML]: Java is Java HotSpot(TM) 64-Bit Server VM, version 1.8.0_172, running on Windows 10:amd64:10.0, installed at C:\Program Files\Java\jre1.8.0_172
[12:45:02] [main/INFO] [FML]: Managed to load a deobfuscated Minecraft name- we are in a deobfuscated environment. Skipping runtime deobfuscation
[12:45:02] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker
[12:45:02] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLDeobfTweaker
[12:45:02] [main/INFO] [LaunchWrapper]: Calling tweak class cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker
[12:45:02] [main/ERROR] [LaunchWrapper]: Unable to launch
java.util.ConcurrentModificationException
	at java.util.ArrayList$Itr.checkForComodification(Unknown Source) ~[?:1.8.0_172]
	at java.util.ArrayList$Itr.remove(Unknown Source) ~[?:1.8.0_172]
	at net.minecraft.launchwrapper.Launch.launch(Launch.java:117) [launchwrapper-1.9.jar:?]
	at net.minecraft.launchwrapper.Launch.main(Launch.java:28) [launchwrapper-1.9.jar:?]

There is no errors in my code, and I am using the source files on files.minecraftforge.net for 1.7.2. Please tell me what I did wrong