Extra options break multipart upload logic

[wmagda]

I'm trying to add ServerSideEncryption option:
var ws = S3S.WriteStream(core.S3Client, { ServerSideEncryption: 'AES256', Bucket: bucketName, Key: fileName });

However that results in this error at the end of upload:
Unhandled rejection UnexpectedParameter: Unexpected key 'ServerSideEncryption' found in params.MultipartUpload.Parts[0]

That's because of this code in MultipartUpload.prototype.uploadPart:
return (err) ? reject(err) : resolve(_.assign({ }, result, { PartNumber: partNumber }));

The problem here is that the extra option is returned as part of result and then you pass that option to Parts array. Parts array can only have ETag and PartNumber resulting in this error.