Do not attempt to decorate nil logs

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## dev
 
+- **Bugfix: Do not attempt to decorate logs with `nil` messages**
+
+  The agent no longer attempts to add New Relic linking metadata to logs with `nil` messages. Thank you, [@arlando](https://github.com/arlando) for bringing this to our attention! [Issue#2985](https://github.com/newrelic/newrelic-ruby-agent/issues/2985) [PR#2986](https://github.com/newrelic/newrelic-ruby-agent/pull/2986)
+
 - **Bugfix: Stop renaming final Grape segment**
 
   Previously, the agent renamed the final segment in Grape transactions to `"Middleware/Grape/#{class_name}/call"`. This was a part of an old instrumentation pattern that is no longer relevant. Many thanks to [@seriousdev-gh](https://github.com/seriousdev-gh) for bringing this issue to our attention and along with a great reproduction and suggested fix. [PR#2987](https://github.com/newrelic/newrelic-ruby-agent/pull/2987).

lib/new_relic/agent/local_log_decorator.rb

@@ -9,7 +9,7 @@ module LocalLogDecorator
       extend self
 
       def decorate(message)
-        return message unless decorating_enabled?
+        return message if !decorating_enabled? || message.nil?
 
         metadata = NewRelic::Agent.linking_metadata
 

test/new_relic/agent/local_log_decorator_test.rb

@@ -77,6 +77,13 @@ def test_decorates_if_enabled
         assert_equal decorated_message, "#{MESSAGE} #{METADATA_STRING}"
       end
 
+      def test_does_not_decorate_if_message_is_nil
+        metadata_stubs
+        decorated_message = LocalLogDecorator.decorate(nil)
+
+        assert_nil(decorated_message)
+      end
+
       def test_decorate_puts_metadata_at_end_of_first_newline
         metadata_stubs
         message = "This is a test of the Emergency Alert System\n this is only a test...."