private StringBuilder mergeKeyValuePairs(List<KeyValuePair> keyValuePairList, StringBuilder sb) {
        if(keyValuePairList == null || keyValuePairList.isEmpty())
            return sb;

        if(sb == null)
            sb = new StringBuilder();

        for(KeyValuePair kvp : keyValuePairList) {
            sb.append(kvp.key);
            sb.append('=');
            sb.append(kvp.value);
            sb.append(' ');
        }
        return sb;
    }
Prepend markers and key-value pairs to the message.

@param aLoggingEvent

@return
slf4j-api/src/main/java/org/slf4j/spi/DefaultLoggingEventBuilder.java