Nunjucks templates don't work across lines in the custom labels

[brandoningli]

Issue

When a nunjucks template spans multiple lines in the custom labels, nothing renders.

Example

Broken:

{% if state == "playing" %}
{{media_title}}
{{app_name}}
{% else %}
{{state|capitalize}}
{% endif %}

Works:

{% if state == "playing" %}{{media_title}}{{- '\n' -}}{{app_name}}{% else %}{{state|capitalize}}{% endif %}

Current Behavior

The custom label does not render; the HA icon does

Expected Behavior

The template renders as typed even if it spans multiple lines