logback-android/src/main/java/ch/qos/logback/classic/util/LogbackMDCAdapter.java
public Set<String> getKeys() {
    Map<String, String> map = getPropertyMap();

    if (map != null) {
      return map.keySet();
    } else {
      return null;
    }
  }
public Set<String> getKeys() {
    Map<String, String> map = getPropertyMap();

    if (map != null) {
      return map.keySet();
    } else {
      return null;
    }
  }
Returns the keys in the MDC as a {@link Set}. The returned value can be
null.