@Override
    public String popByKey(String key) {
        return null;
    }
This adapter is an empty implementation of the {@link MDCAdapter} interface.
It is used for all logging systems which do not support mapped
diagnostic contexts such as JDK14, simple and NOP. 

@author Ceki G&uuml;lc&uuml;

@since 1.4.1
slf4j-api/src/main/java/org/slf4j/helpers/NOPMDCAdapter.java