local-class={{this.size}} throws an error, but local-class="{{this.size}}" is ok

[gvocale]

In a glimmer component, using ember-css-modules, why the following?

import Component from '@glimmer/component';

enum Size {
  Sm = 'sm',
  Md = 'md',
}

interface Args {
  size: Size;
}

export default class Logo extends Component<Args> {
  size: Size;

  constructor(owner: unknown, args: Args) {
    super(owner, args);
    this.size = this.args.size || Size.Md;
  }
}

{{this.size}} // outputs sm
<div local-class={{this.size}}> // throws error Uncaught (in promise) Error: Compile Error: size 
is not a helper
  <UiIcon @name='logo' />
</div>

In particular, using local-class={{this.size}} throws the error:

Uncaught (in promise) Error: Compile Error: size is not a helper

But instead, using local-class="{{this.size}}" works ok

[lolmaus]

Duplicate of #132?