Don't include Google Analytics scripts without analytics id (#482)

_config.yml

@@ -49,13 +49,13 @@ social:
     # - https://www.facebook.com/username
     # - https://www.linkedin.com/in/username
 
-google_site_verification: google_meta_tag_verification # change to your verification string
+google_site_verification:               # fill in to your verification string
 
 # ↑ --------------------------
 
 
 google_analytics:
-  id: ''              # fill in your Google Analytics ID
+  id:                 # fill in your Google Analytics ID
   # Google Analytics pageviews report settings
   pv:
     proxy_endpoint:   # fill in the Google Analytics superProxy endpoint of Google App Engine

_includes/head.html

@@ -40,7 +40,8 @@
   <link rel="dns-prefetch" href="https://fonts.gstatic.com">
 
   <!-- GA -->
-  {% if jekyll.environment == 'production' %}
+  {% if jekyll.environment == 'production'
+      and site.google_analytics.id != empty and site.google_analytics.id %}
     <link rel="preconnect" href="https://www.google-analytics.com" crossorigin="use-credentials">
     <link rel="dns-prefetch" href="https://www.google-analytics.com">
 

_includes/js-selector.html

@@ -61,7 +61,7 @@
   <script defer src="{{ '/app.js' | relative_url }}"></script>
 
   <!-- GA -->
-  {% if site.google_analytics.id %}
+  {% if site.google_analytics.id != empty and site.google_analytics.id %}
     {% include google-analytics.html %}
   {% endif %}
 

assets/js/data/swcache.js

@@ -43,7 +43,7 @@ const resource = [
 
 /* The request url with below domain will be cached */
 const allowedDomains = [
-  {% if site.google_analytics.id != '' %}
+  {% if site.google_analytics.id != empty and site.google_analytics.id %}
     'www.googletagmanager.com',
     'www.google-analytics.com',
   {% endif %}