give get() default values

[Eusen]

The second parameter of the method is used as the default value to minimize code changes
this.editor.config.get( 'blockToolbar', [] );

afterInit() {
        const factory = this.editor.ui.componentFactory;
        const config = this.editor.config.get( 'blockToolbar', [] );

        this.toolbarView.fillFromConfig( config, factory );

        // Hide panel before executing each button in the panel.
        for ( const item of this.toolbarView.items ) {
                item.on( 'execute', () => this._hidePanel( true ), { priority: 'high' } );
        }
}

[jodator]

As described in other PR I think that for now we're safe with || check. The previous proposal was to add a default value by the existing API:

editor.config.define( 'blockToolbar', [] );

so subsequent calls to editor.config.get( 'blockToolbar' ) will not blow up the editor if no configuration blockToolbar is pased to the editor as in your case.

I'm closing this in favor of: ckeditor/ckeditor5-ui#534 since at the moment we don't want to add additional params to the API as we can achieve the same things otherwise and the config.get() || defaultValue is used already elsewhere.

Thanks for the input :)