Problems accessing subscription information at checkout (using checkout.liquid)

[joelp]

Shopify Plus store dev here, just diving in to checkout.liquid modifications for the first time and I'm having trouble pulling subscription and metafield data out of checkout.line_items. 

I'd like to know if a product is being purchased on a subscription basis. However, line_item.selling_plan_allocation always seems to be nil, so the below outputs nothing. 

{%- for line_item in checkout.line_items -%}
  {%- if line_item.selling_plan_allocation != nil -%}
    {{ line_item.product.title }} has selling plan name {{ line_item.selling_plan_allocation.selling_plan.name }}.
  {%- endif -%}
{%- endfor -%}

How should I be accessing the selling plan information for products in the order? Thanks for any help.