AWS S3 SDK source code is showing completeMultipartUpload() with UnsupportedOperationException

Question

I am trying to use AWS S3 SDK 2.13 and seeing the completeMultipartUpload method is implemented like this in their source code -

default CompleteMultipartUploadResponse completeMultipartUpload(CompleteMultipartUploadRequest completeMultipartUploadRequest)
   throws AwsServiceException, SdkClientException, S3Exception {
        throw new UnsupportedOperationException();
}

I am surprised to see that such obvious apis are not implemented in s3 sdk 2+ versions but their documentation shows usage of it - https://github.com/awsdocs/aws-doc-sdk-examples/blob/master/javav2/example_code/s3/src/main/java/com/example/s3/S3ObjectOperations.java#L210 https://docs.aws.amazon.com/sdk-for-java/v2/developer-guide/examples-s3-objects.html

I even tried downloading and seeing the source code in decompiler for 2.14 version and it's the same - decompiler s3 sdk code

I am not sure whether I am looking at it right because it's vey unlikely that AWS is missing such widely used functionality in most of their recent versions.

note- I am importing aws sdk s3 dependency using sbt -

"software.amazon.awssdk" % "s3" % "2.13.8"