Why did the lower built in filter not work in Django template 2.2? - django

Question

Using Django v2.2 built-in filters for templates.
my template looks like this:
{% load i18n %}{% blocktrans with site_name=current_site.organization.name site_domain=current_site.name %}Hello from {{ site_name }}!
You're receiving this e-mail because your email is subscribed to receiving notification when a Quotation is Pending PO Release.
{{ quote_type }}
{{ quote_type|lower }}
- Quotation: {{ display_quotation_number }}
- PO Date: {{ po_date_display }} (New)
{% endblocktrans %}
{% blocktrans with site_name=current_site.organization.name site_domain=current_site.name %}Thank you for using {{ site_name }}!
{{ site_domain }}{% endblocktrans %}
I can say with certainty that {{ quote_type }} definitely prints something out. {{ quote_type|lower }} prints nothing.
What did I do wrong?
I was certain that the filter is builtin; see https://docs.djangoproject.com/en/2.2/ref/templates/builtins/#lower
UPdate
This is my current workard and it works
extra_context = self.lower_quote_type(extra_context)
quotation.email_people(
recipient_list=recipient_list,
extra_context=extra_context,
)
def lower_quote_type(self, extra_context):
# #makeAnIssue temp workard for #1334 but try to permanently fix it elegantly
if "quote_type" in extra_context:
extra_context["quote_type"] = extra_context["quote_type"].lower()
return extra_context
Then this works
{% load i18n %}{% blocktrans with site_name=current_site.organization.name site_domain=current_site.name %}Hello from {{ site_name }}!
You're receiving this e-mail because your email is subscribed to receiving notification when a Quotation is Pending PO Release.
{{ quote_type }} # this correctly shows up as lower case
- Quotation: {{ display_quotation_number }}
- PO Date: {{ po_date_display }} (New)
{% endblocktrans %}
{% blocktrans with site_name=current_site.organization.name site_domain=current_site.name %}Thank you for using {{ site_name }}!
{{ site_domain }}{% endblocktrans %}