ConcurrentModificationException in the class cache

[derrop]

Description
Sometimes the class cache throws a ConcurrentModificationException when transforming classes which crashes the client:

Log Output

Caused by: net.flintmc.transform.exceptions.ClassTransformException: transform threw an exception
	at net.flintmc.transform.javassist.internal.DefaultMethodBasedClassTransformMeta.execute(DefaultMethodBasedClassTransformMeta.java:113)
	at net.flintmc.transform.javassist.internal.DefaultClassTransformService.transform(DefaultClassTransformService.java:163)
	at net.flintmc.transform.launchplugin.FlintLauncherPlugin.modifyClass(FlintLauncherPlugin.java:153)
	at net.flintmc.launcher.classloading.RootClassLoader.findClass(RootClassLoader.java:241)
	at net.flintmc.launcher.classloading.RootClassLoader.findClass(RootClassLoader.java:145)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
	at e.<init>(SourceFile:21)
	at e.<clinit>(SourceFile:8)
	... 52 more
Caused by: java.lang.reflect.InvocationTargetException
	at sun.reflect.GeneratedMethodAccessor6.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:497)
	at net.flintmc.transform.javassist.internal.DefaultMethodBasedClassTransformMeta.execute(DefaultMethodBasedClassTransformMeta.java:107)
	... 60 more
Caused by: java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.nextNode(HashMap.java:1429)
	at java.util.HashMap$EntryIterator.next(HashMap.java:1463)
	at java.util.HashMap$EntryIterator.next(HashMap.java:1461)
	at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.write(MapTypeAdapterFactory.java:206)
	at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.write(MapTypeAdapterFactory.java:145)
	at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:69)
	at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:127)
	at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:245)
	at com.google.gson.Gson.toJson(Gson.java:704)
	at com.google.gson.Gson.toJson(Gson.java:683)
	at com.google.gson.Gson.toJson(Gson.java:638)
	at com.google.gson.Gson.toJson(Gson.java:618)
	at net.flintmc.util.classcache.internal.DefaultClassCacheIndex.write(DefaultClassCacheIndex.java:93)
	at net.flintmc.util.classcache.internal.DefaultClassCache.writeClass(DefaultClassCache.java:94)
	at net.flintmc.util.classcache.internal.DefaultClassCache.getOrTransformAndWriteClass(DefaultClassCache.java:108)
	at net.flintmc.transform.minecraft.obfuscate.MinecraftInstructionObfuscator.transform(MinecraftInstructionObfuscator.java:85)
	at net.flintmc.transform.launchplugin.FlintLauncherPlugin.modifyClass(FlintLauncherPlugin.java:153)
	at net.flintmc.launcher.classloading.RootClassLoader.findClass(RootClassLoader.java:241)
	at net.flintmc.launcher.classloading.RootClassLoader.findClass(RootClassLoader.java:145)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:348)
	at net.flintmc.transform.shadow.internal.ShadowHelper.getLocation(ShadowHelper.java:63)
	at net.flintmc.transform.shadow.internal.handler.defaults.ShadowGetterHandler.transform(ShadowGetterHandler.java:57)
	at net.flintmc.transform.shadow.internal.ShadowService.transformMethods(ShadowService.java:110)
	at net.flintmc.transform.shadow.internal.ShadowService.transform(ShadowService.java:101)
	... 64 more

System Information:

• Operating System: Windows 10
• Launcher: Official
• Flint Version: 2.0.36
• Minecraft Versions: 1.16.5
• Java Version: Launcher bundled