Using populated fields in virtuals: How do you type the field in the schema?

Question

I have a Typescript project using mongoose that has a virtual that depends on a field that has been populated from a middleware function. I am having some trouble figuring out how to type things properly.

const UserSchema = new Schema({
   someid: String,
   email: String,
   roles: {
     type: Schema.Types.ObjectId,
     ref: 'Role'
   }
)}

UserSchema.pre<Query>(/^find/, autopopulate);

function autopopulate(next){
  this.populate('roles'); // I assume at runtime the roles field is overwritten to be an array of `RoleInterface` objects, rather than an array of ObjectIds. How does Typescript deal with this?
  next();
}

UserSchema.virtual('isAdmin').get(function () {
  return this.roles[1].name === 'admin'; //this.roles is [{_id: ObjectId}] as defined in the schema, so this fails the typecheck
});

The issue is that name is not a field of role in the schema as written, it's a field in the populated version of the schema from the pre hook. What is the correct way to type things so that this will work?