allow stats cb reset (#342)

Author: mensfeld

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Rdkafka Changelog
 
 ## 0.14.0 (Unreleased)
+- [Enhancement] Allow for setting `statistics_callback` as nil to reset predefined settings configured by a different gem (mensfeld)
 * [Enhancement] Get consumer position (thijsc & mensfeld)
 * [Enhancement] Provide `#purge` to remove any outstanding requests from the producer (mensfeld)
 * [Enhancement] Update `librdkafka` to `2.2.0` (mensfeld)

lib/rdkafka/config.rb

@@ -57,7 +57,7 @@ def self.logger=(logger)
     #
     # @return [nil]
     def self.statistics_callback=(callback)
-      raise TypeError.new("Callback has to be callable") unless callback.respond_to?(:call)
+      raise TypeError.new("Callback has to be callable") unless callback.respond_to?(:call) || callback == nil
       @@statistics_callback = callback
     end