Duplicate empty header names are allowed even with `.withAllowDuplicateHeaderNames(false)`

I'm trying to parse to parse a csv like this:

CSVFormat.DEFAULT
{{ .withHeader()}}
{{ .withAllowDuplicateHeaderNames(false)}}
{{ .withAllowMissingColumnNames()}}
{{ .parse(InputStreamReader(FileInputStream(fl)))}}

One would expect this code to throw an error if the following csv is given as input:

"","a",""

"1","X","3"

"3","Y","4"

But it doesn't, and asking for `record.get("")` gives the value from the second column. The first column is ignored.