如何在NLog中设置isdebugenabled

<?xml version="1.0" encoding="utf-8" ?>
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

 <targets>
   <target name="debug" xsi:type="Debugger" layout="${message}" />
  </targets>

 <rules>
   <logger name="*" minlevel="Debug" writeTo="debug" />
  </rules>
</nlog>

private static Logger logger = LogManager.GetCurrentClassLogger();

public void SomeMethod()
{
    if (logger.IsDebugEnabled)
    {
        logger.Debug("This is a debug message.");
    }
}