Help with registering ArgumentType

[Aes123]

Hi, i'm making a new command which requires a new argumentType called StringPlusArgumentType. I have effectively copied StringArgumentType and only changed it so '=' is considered a valid character. I'm having trouble registering it.

    public static final DeferredRegister<ArgumentTypeInfo<?,?>> ARGUMENT_TYPES = DeferredRegister.create(ForgeRegistries.COMMAND_ARGUMENT_TYPES, MODID);
    public static final RegistryObject<ArgumentTypeInfo<?,?>> STRING_PLUS_ARGUMENT_TYPE = ARGUMENT_TYPES.register("string_plus", () -> new StringPlusArgumentSerializer());

And then:

ARGUMENT_TYPES.register(modEventBus);
MinecraftForge.EVENT_BUS.register(this);

But when i try to join a world it crashes with the message "Invalid player data"

Crash log:

java.lang.IllegalArgumentException: Unrecognized argument type string() (class me.aes123.commands_plus.commands.StringPlusArgumentType)
	at net.minecraft.commands.synchronization.ArgumentTypeInfos.byClass(ArgumentTypeInfos.java:155)

[ChampionAsh5357]

See ArgumentTypeInfos#registerByClass.