# File lib/new_relic/agent/configuration/manager.rb, line 154
        def invoke_callbacks(direction, source)
          return unless source
          source.keys.each do |key|

            if @cache[key] != source[key]
              @callbacks[key].each do |proc|
                if direction == :add
                  proc.call(source[key])
                else
                  proc.call(@cache[key])
                end
              end
            end
          end
        end