Bug 26940: Take empty strings into account

Signed-off-by: Katariina Hanhisalo <katariina.hanhisalo@xamk.fi>

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 789ddd59c9)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>

installer/data/mysql/atomicupdate/bug_26940.perl

@@ -4,7 +4,7 @@ if( CheckVersion( $DBversion ) ) {
         SELECT d.borrowernumber, GROUP_CONCAT(comment SEPARATOR '\n') AS comment
         FROM borrower_debarments d
         LEFT JOIN borrowers b ON b.borrowernumber=d.borrowernumber
-        WHERE b.debarredcomment IS NULL AND ( expiration > CURRENT_DATE() OR expiration IS NULL )
+        WHERE ( b.debarredcomment IS NULL OR b.debarredcomment = "" ) AND ( expiration > CURRENT_DATE() OR expiration IS NULL )
         GROUP BY d.borrowernumber
     |, { Slice => {} });