An alternative to Joost's solution is to set the RaiseError flag to true, causing DBI to throw an exception instead of retuning undef. However, avoiding RaiseError allows you to provide a more meaningful error message.

For example, the following dies with a meaninful error message on error. It also only reads one row since that's all you want.

my $ref = $dbh->selectcol_arrayref($query)
   or die("Unable to fetch blog name: ",
          $DBI::err || "Unknown database error",
          "\n");

$param{welcome} = $ref->[0];
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Update: Added example.