lib/opentelemetry/common/propagation/rack_env_getter.rb in opentelemetry-common-0.20.0 vs lib/opentelemetry/common/propagation/rack_env_getter.rb in opentelemetry-common-0.20.1

@@ -27,10 +27,11 @@
         end
 
         private
 
         def to_rack_key(key)
-          ret = "HTTP_#{key}"
+          # Use + for mutable string interpolation in pre-Ruby 3.0.
+          ret = +"HTTP_#{key}"
           ret.tr!('-', '_')
           ret.upcase!
           ret
         end