Grails Excel plugin how to import all sheets?

Grails Excel plugin how to import all sheets?

The Excel-import plugin (http://grails.org/plugin/excel-import) is very
easy to use, but when importing a file I have to specify the exact name of
the sheet. But when I want to import many files i don't always know their
names. I didn't find any info on how to automatically import without
specifying the exact name...
static Map CONFIG_BOOK_COLUMN_MAP = [
sheet:'Sheet1',
startRow: 2,
columnMap: [
'B':'title',
'C':'author',
'D':'numSold',
]
]
When i remove the "sheet" parameter unfortunately nothing gets
imported...is there a way to do this?