private void initialize() {
        fillRate = null;
        maxCapacity = null;
        currentCapacity = 0.0;
        lastTimestamp = null;
        enabled = false;
        measuredTxRate = 0.0;
        lastTxRateBucket = Math.floor(clock.time());
        requestCount = 0;
        lastMaxRate = 0.0;
        lastThrottleTime = clock.time();
    }
@param amount The amount of capacity to acquire from the bucket.
@return The unfulfilled amount.
aws-java-sdk-core/src/main/java/com/amazonaws/internal/TokenBucket.java