my @hdr = $csv->header ($fh, {
    munge_column_names => sub { state $i; $_ || "nothing.".$i++ }});

##</code><code>##

Volume.label
Volume.serialno
Volume.vtype
Volume.netname
Volume.filesystem
Path.name
nothing.0
Thumbnail.checksum
Thumbnail.width
Thumbnail.height
Thumbnail.horiz_res
Thumbnail.vert_res
Thumbnail.colortype
Thumbnail.colordepth
Thumbnail.gamma
Thumbnail.thumbnail_width
Thumbnail.thumbnail_height
Thumbnail.thumbnail_type
Thumbnail.thumbnail_size
Thumbnail.name
Thumbnail.metric1
Keywords.pkeywords
nothing.1