# File lib/new_relic/agent/configuration/yaml_source.rb, line 114
        def substitute_transaction_threshold(config)
          if config['transaction_tracer'] &&
              config['transaction_tracer']['transaction_threshold'] =~ /apdex_f/i
            # when value is "apdex_f" remove the config and defer to default
            config['transaction_tracer'].delete('transaction_threshold')
          end
        end