If your database column contains a NULL in this column then $value_a will contain the Perl value "undef". The warning you are getting is saying that you are trying to match a regular expression against an undefined variable.

You probably want to change the code to something more like this:

if (defined $value_a) {
  if($value_a =~/personal/) {
    $value_a = "checked";
  } else {
    $value_a = '';
  } 
} else {
  $value_a = '';
}
[download]

You should also consider whether you really want to check the value of the variable using a regex match. If you just want to check that the value is "checked", then using the string equality operator will be more efficient.

if (defined $value_a) {
  if($value_a eq 'personal') {
    $value_a = 'checked';
  } else {
    $value_a = '';
  } 
} else {
  $value_a = '';
}
[download]

Update: Fixed a couple of typos (thanks johngg)