question: public static void updateServerTimestampHeader ( MultiMap headers ) { String serverTimestamp = headers . get ( SERVER_TIMESTAMP_HEADER ) ; if ( serverTimestamp == null ) { String nowAsISO = dfISO8601 . print ( Instant . now ( ) ) ; log . debug ( "Setting " + SERVER_TIMESTAMP_HEADER + " value to " + nowAsISO + "  since header " + SERVER_TIMESTAMP_HEADER + " is not defined" ) ; headers . set ( SERVER_TIMESTAMP_HEADER , nowAsISO ) ; } else { String updatedTimestamp = localizeTimestamp ( serverTimestamp ) ; if ( ! updatedTimestamp . equals ( serverTimestamp ) ) { log . debug ( "Updating" + SERVER_TIMESTAMP_HEADER + " value from " + serverTimestamp + "  to " + updatedTimestamp ) ; headers . remove ( SERVER_TIMESTAMP_HEADER ) ; headers . set ( SERVER_TIMESTAMP_HEADER , updatedTimestamp ) ; } } }
target:  Checks if a "X-Server-Timestamp" header is set or not. If no valid value is found, the actual timestamp is set.