Fix LinkCrawlWorker NoMethodError: undefined method `[]' for nil (#31144)

app/lib/link_details_extractor.rb

@@ -101,7 +101,7 @@ class LinkDetailsExtractor
     end
 
     def json
-      @json ||= root_array(Oj.load(@data)).find { |obj| SUPPORTED_TYPES.include?(obj['@type']) } || {}
+      @json ||= root_array(Oj.load(@data)).compact.find { |obj| SUPPORTED_TYPES.include?(obj['@type']) } || {}
     end
   end
 

spec/lib/link_details_extractor_spec.rb

@@ -129,6 +129,24 @@ RSpec.describe LinkDetailsExtractor do
       include_examples 'structured data'
     end
 
+    context 'with the first tag is null' do
+      let(:html) { <<~HTML }
+        <!doctype html>
+        <html>
+        <body>
+          <script type="application/ld+json">
+            null
+          </script>
+          <script type="application/ld+json">
+            #{ld_json}
+          </script>
+        </body>
+        </html>
+      HTML
+
+      include_examples 'structured data'
+    end
+
     context 'with preceding block of unsupported LD+JSON' do
       let(:html) { <<~HTML }
         <!doctype html>