blob/azblob: Pass nil instead of an empty map for tags on Copy operation (#2989)

Author: vangent

blob/azureblob/azureblob.go

@@ -541,7 +541,6 @@ func (b *bucket) Copy(ctx context.Context, dstKey, srcKey string, opts *driver.C
 	mac := azblob.ModifiedAccessConditions{}
 	bac := azblob.BlobAccessConditions{}
 	at := azblob.AccessTierNone
-	btm := azblob.BlobTagsMap{}
 	if opts.BeforeCopy != nil {
 		asFunc := func(i interface{}) bool {
 			switch v := i.(type) {
@@ -561,7 +560,7 @@ func (b *bucket) Copy(ctx context.Context, dstKey, srcKey string, opts *driver.C
 			return err
 		}
 	}
-	resp, err := dstBlobURL.StartCopyFromURL(ctx, srcURL, md, mac, bac, at, btm)
+	resp, err := dstBlobURL.StartCopyFromURL(ctx, srcURL, md, mac, bac, at, nil /* BlobTagsMap */)
 	if err != nil {
 		return err
 	}