Set instrumentation name

Author: gjtorikian

lib/html/pipeline.rb

@@ -69,7 +69,8 @@ def self.parse(document_or_html)
     # Public: String name for this Pipeline. Defaults to Class name.
     attr_writer :instrumentation_name
     def instrumentation_name
-      @instrumentation_name || self.class.name
+      return @instrumentation_name if defined?(@instrumentation_name)
+      @instrumentation_name = self.class.name
     end
 
     class << self