Liquid template for show all the product types as links does not show anything

Store Design
1

I added the following code as “Custom Liquid” in the page’s theme editor.

111111
{% for product_type in collection.all_types %}
  {{ product_type | link_to_type }}
{% endfor %}

But I only see the 11111 in previous and not the content should be generated by above liquid script.

Anything wrong?