If I have a log4j.xml file that I'm using to init the loggers, with a logger(`foo`) defined in it without any `appender-ref` tags within it, what does this logger do? If it does nothing, does it have an impact on performance?

```
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
  <appender name="console" class="org.apache.log4j.ConsoleAppender"> 
    <param name="Target" value="System.out"/> 
    <layout class="org.apache.log4j.PatternLayout"> 
      <param name="ConversionPattern" value="%-5p %c{1} - %m%n"/> 
    </layout> 
  </appender> 

  <logger name="foo">
    <level value="WARN"/>
  </logger>

  <root> 
    <priority value ="debug" /> 
    <appender-ref ref="console" /> 
  </root>

</log4j:configuration>

```