[BUG/Question] Dropdown indicator not displayed for a custom trait

Hello,

the dropdown (select) element arrow indicator icon is not rendered when adding a custom trait to a component:

I'm using following code to add the custom trait to the link component:

editor.TraitManager.addType('internal-link', {
    // A custom option-loading function
    loadOptions: function (inputEl) {
        foo();
    },
    getInputEl: function () {
        if (!this.inputEl) {
            var input = document.createElement('select');
            this.loadOptions(input);

            this.inputEl = input;
        }
        return this.inputEl;
    },
    onValueChange: function () {
        bar();
    }
});

linkModel.prototype.defaults.traits.push({
    type: 'internal-link',
    label: 'Internal link',
    name: 'internal-link'
})

Is there anything I'm missing? An extra attribute perhaps? Everything else works fine, except for this detail (which is apparently very important to my customer).

I am currently on release 14.6 and I can't find a way how to force GrapesJS to render the dropdown indicator like it does for all default component traits (e. g. link target).