public Object put(String key, Object value) {
      if (value == null) {
        return get(key);
      } else {
        return super.put(key, value);
      }
    }
A helper class that only puts non-null values into the encoded LoggingEvent
map. This helps to shrink over-the-wire byte payloads for encoded
LoggingEvents.
samza-log4j/src/main/java/org/apache/samza/logging/log4j/serializers/LoggingEventJsonSerde.java