Hello guys. I use S3 preSigned URL to upload file, but it return an error "The Content-MD5 you specified was invalid".
It happens only when I generate Presigned Url with contentMd5.However it works fine when I annotation the line '.withContentMd5(md5)'.
My file md5 is 32c295626872e465b3d0b590eb8e88a7.

```java
        AmazonS3 s3client = getDefaultS3Client();
        Date expiration = new Date(System.currentTimeMillis() + expiratMillis);
        GeneratePresignedUrlRequest generatePresignedUrlRequest =
                new GeneratePresignedUrlRequest(bucketName, s3FullPath)
                        .withMethod(HttpMethod.PUT)
                        .withExpiration(expiration)
                        .withKey(s3Key)
                        .withContentMd5(md5);
        String presignedUrl =  s3client.generatePresignedUrl(generatePresignedUrlRequest);
 ```


![postman](https://user-images.githubusercontent.com/4321439/60160341-bdfafd80-9827-11e9-8a26-03ec4c4d8faf.png)

Does S3 support checksum when using presigned url?
Could anybody give me a piece of advice to help me solve this? Thank you!
record['eventName'] = 'REMOVE'
                record['dynamodb']['Keys'] = data['Key']
                record['dynamodb']['OldImage'] = old_item
        elif action == '%s.CreateTable' % ACTION_PREFIX:
            if 'StreamSpecification' in data:
                if response.status_code == 200:
                    content = json.loads(to_str(response._content))
                    create_dynamodb_stream(data, content['TableDescription'].get('LatestStreamLabel'))
            event_publisher.fire_event(event_publisher.EVENT_DYNAMODB_CREATE_TABLE,
                payload={'n': event_publisher.get_hash(data['TableName'])})
            return
        elif action == '%s.DeleteTable' % ACTION_PREFIX:
            event_publisher.fire_event(event_publisher.EVENT_DYNAMODB_DELETE_TABLE,
                payload={'n': event_publisher.get_hash(data['TableName'])})
            return
        elif action == '%s.UpdateTable' % ACTION_PREFIX:
            if 'StreamSpecification' in data:
                if response.status_code == 200:
                    content = json.loads(to_str(response._content))
                    create_dynamodb_stream(data, content['TableDescription'].get('LatestStreamLabel'))
            return
        else:
            
            return
        if len(records) > 0 and 'eventName' in records[0]:
            if 'TableName' in data:
                records[0]['eventSourceARN'] = aws_stack.dynamodb_table_arn(data['TableName'])
            forward_to_lambda(records)
            forward_to_ddb_stream(records)
    def prepare_batch_write_item_records(self, record, data):