InvalidTypeError: Type is invalid! Type is: "undefined"

Versions

• typegoose: 7.3.0
• mongoose: 5.9.24

Using the following definition for UserClass:

@pre<UserClass>("save", async function (next: HookNextFunction): Promise<void> {
    ...
})
@index({ name: 1 }, { collation: { locale: "en", strength: 1 }, unique: true })
export class UserClass {
    @prop({
        required: true,
        trim: true,
        unique: true,
        minlength: 3,
        maxlength: 20
    })
    public name!: string;
...
}

I get the following unhelpful error:

@typegoose\typegoose\lib\internal\processProp.js:160
        throw new errors_1.InvalidTypeError(name, key, Type);
        ^

InvalidTypeError: "UserClass.name"'s Type is invalid! Type is: "undefined"
    at Object.processProp (C:\Users\winterNebs\source\repos\AscensionGame\AscensionGame\node_modules\@typegoose\typegoose\lib\internal\processProp.js:160:15)
    at Object._buildSchema (C:\Users\winterNebs\source\repos\AscensionGame\AscensionGame\node_modules\@typegoose\typegoose\lib\internal\schema.js:37:27)
    at buildSchema (C:\Users\winterNebs\source\repos\AscensionGame\AscensionGame\node_modules\@typegoose\typegoose\lib\typegoose.js:120:20)
    at Object.getModelForClass (C:\Users\winterNebs\source\repos\AscensionGame\AscensionGame\node_modules\@typegoose\typegoose\lib\typegoose.js:70:39)
    at Object../database/schema/user.ts (C:\Users\winterNebs\source\repos\AscensionGame\AscensionGame\dist\app.js:2121:28)
    at __webpack_require__ (C:\Users\winterNebs\source\repos\AscensionGame\AscensionGame\dist\app.js:20:30)
    at Object../gameAppServer.ts (C:\Users\winterNebs\source\repos\AscensionGame\AscensionGame\dist\app.js:2409:16)
    at __webpack_require__ (C:\Users\winterNebs\source\repos\AscensionGame\AscensionGame\dist\app.js:20:30)
    at Object../app.ts (C:\Users\winterNebs\source\repos\AscensionGame\AscensionGame\dist\app.js:1351:25)
    at __webpack_require__ (C:\Users\winterNebs\source\repos\AscensionGame\AscensionGame\dist\app.js:20:30)
    at C:\Users\winterNebs\source\repos\AscensionGame\AscensionGame\dist\app.js:84:18
    at Object.<anonymous> (C:\Users\winterNebs\source\repos\AscensionGame\AscensionGame\dist\app.js:87:10)
    at Module._compile (internal/modules/cjs/loader.js:955:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:991:10)
    at Module.load (internal/modules/cjs/loader.js:811:32)
    at Function.Module._load (internal/modules/cjs/loader.js:723:14)

As far as I can tell the type for name is string, not undefined. Can anyone spot what I did wrong or is this error not related to this code?

I migrated from ts-mongoose since that project doesn’t look like its being updated anymore, so sorry that I don’t have a very minimal example.