Return TBU image path in JSON API if its thumbnail not given yet

Author: yasulab

_includes/projects2json.json

@@ -1,9 +1,11 @@
+{% capture default_thumbnail_path %}/assets/img/projects/{{ pj.year }}/{{ pj.id }}.webp{% endcapture %}
+{% capture default_thumbnail_exists %}{% file_exists default_thumbnail_path %}{% endcapture %}
 [ {% for pj in projects %}
   {
     "id"          : "{{ pj.id }}",
     "title"       : "{{ pj.title }}",
     "description" : "{{ pj.description | escape }}",
-    "thumbnail"   : "{{ site.url }}/assets/img/projects/{{ pj.year }}/{% if pj.thumbnail %}{{ pj.thumbnail }}{% else %}{{ pj.id}}.webp{% endif %}",
+    "thumbnail"   : "{{ site.url }}/assets/img/projects/{{ pj.year }}/{% if pj.thumbnail %}{{ pj.thumbnail }}{% elsif default_thumbnail_exists %}../tbu.webp{% else %}{{ pj.id }}.webp{% endif %}",
     "url"         : "{{ site.url }}/projects/{{ pj.year }}/{{ pj.id }}",
     "year"        : "{{ pj.year }}",
     "creators"    : [

projects/search.json

@@ -3,12 +3,14 @@ layout: null
 ---
 
 {% assign projects  = site.data.projects %}
+{% capture default_thumbnail_path %}/assets/img/projects/{{ pj.year }}/{{ pj.id }}.webp{% endcapture %}
+{% capture default_thumbnail_exists %}{% file_exists default_thumbnail_path %}{% endcapture %}
 
 [ {% for pj in projects %}
   {
     "title"       : "{{ pj.title | escape }}",
     "description" : "{{ pj.description | strip_html | escape }}",
-    "thumbnail"   : "{{ site.url }}/assets/img/projects/{{ pj.year }}/{% if pj.thumbnail %}{{ pj.thumbnail }}{% else %}{{ pj.id}}.webp{% endif %}",
+    "thumbnail"   : "{{ site.url }}/assets/img/projects/{{ pj.year }}/{% if pj.thumbnail %}{{ pj.thumbnail }}{% elsif default_thumbnail_exists %}../tbu.webp{% else %}{{ pj.id }}.webp{% endif %}",
     "permalink"   : "{{ site.url }}/projects/{{ pj.year }}/{{ pj.id }}",
     "year"        : "{{ pj.year }}",
     "creators"    : "{% for creator_id in pj.creator_ids %}{% assign creator = site.data.creators | find_exp: 'item', 'item.id == creator_id' %}{{ creator.name }}{% unless forloop.last %} / {% endunless %}{% endfor %}",