Were that the case I'd expect he would be getting an error trying to call the method Value on an undefined value (at least a quick test referencing a cell from an empty sheet in an existing xls file returns undef for me and $sheet->{Cells} is an arrayref with the 0th item being an empty arrayref (so [ [] ])). Never the less you might want to sanity check your indexen versus $sheet->{MaxRow} and $sheet->{MaxCol} (and/or the minimums if you're truly paranoid :), and also check that you've got a defined value before attempting to manipulate it.

my $value;
if( my $cell = $sheet->{Cell}->[$r]->[$c] ) {
  $value = $cell->Value();
}
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