Otherwise it prints None there and that's everything but desired.
<header><nav id="navigation">
<div class="m-container">
<div class="m-row">
- {% if MAIN_PROJECT_URL and PROJECT_TITLE %}
+ {% if MAIN_PROJECT_URL and PROJECT_SUBTITLE %}
<span id="m-navbar-brand" class="m-col-t-8 m-col-m-none m-left-m">
<a href="{{ MAIN_PROJECT_URL }}">{% if PROJECT_LOGO %}<img src="{{ PROJECT_LOGO|format_url|e }}" />{% endif %}{{ PROJECT_TITLE }}</a> <span class="m-breadcrumb">|</span> <a href="{{ 'index'|path_to_url }}" class="m-thin">{{ PROJECT_SUBTITLE }}</a>
</span>