One possible solution would be to make sure you check that the cell value is in fact numeric (or an integer as shown below) before you use in a calculation: 
$ perl
use strict;
use warnings;
use Data::Table;

my $t = new Data::Table([ [ 1, 2, 3 ], [ 10, 20, " " ] ], [ 'A', 'B' ]
+, 1);

# create emtpy column
my @newCol = ();
$newCol[ $t->nofRow - 1 ] = undef;
$t->addCol(\@newCol, 'adding_up');

# Put the formula in the empty column
$t->colsMap(
  sub {
    $_->[2] =
      ((defined($_->[0]) && $_->[0] =~ m/^\d+$/) ? $_->[0] : 0) +
      ((defined($_->[1]) && $_->[1] =~ m/^\d+$/) ? $_->[1] : 0);
  }
);
print $t->csv;

__END__
A,B,adding_up
1,10,11
2,20,22
3, ,3

[download]
See also How do I determine whether a scalar is a number/whole/integer/float?.
--
Andreas

In reply to Re: Data::Table - empty values - avoid warnings by andreas1234567
in thread Data::Table - empty values - avoid warnings by GertMT

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