Run this plugin only for gem-based themes

lib/jekyll-data.rb

@@ -10,7 +10,16 @@
 require_relative "jekyll/theme"
 require_relative "jekyll/drops/unified_payload_drop"
 
-# replace Jekyll::Reader with a subclass Jekyll::ThemeReader
+# replace Jekyll::Reader with a subclass Jekyll::ThemeReader only if the site
+# uses a gem-based theme else have this plugin disabled.
 Jekyll::Hooks.register :site, :after_init do |site|
-  site.reader = Jekyll::ThemeReader.new(site)
+  if site.theme
+    site.reader = Jekyll::ThemeReader.new(site)
+  else
+    Jekyll.logger.abort_with(
+      "JekyllData:",
+      "Error! This plugin only works with gem-based jekyll-themes. " \
+      "Please disable this plugin to proceed."
+    )
+  end
 end

lib/jekyll/theme_reader.rb

@@ -13,20 +13,15 @@ def initialize(site)
     #
     # Returns nothing.
     def read
-      @site.layouts = LayoutReader.new(site).read
-      read_directories
-      sort_files!
-      @site.data = DataReader.new(site).read(site.config["data_dir"])
+      super
       read_theme_data
-      CollectionReader.new(site).read
-      ThemeAssetsReader.new(site).read
     end
 
     # Read data files within a theme gem and add them to internal data
     #
     # Returns a hash appended with new data
     def read_theme_data
-      if site.theme && site.theme.data_path
+      if site.theme.data_path
         #
         # show contents of "<theme>/_data/" dir being read while degugging.
         # Additionally validate if a data file with the same name as the