Fixing pages warning when value is null

htdocs/accountancy/admin/accountmodel.php

htdocs/accountancy/admin/categories_list.php

htdocs/accountancy/admin/journals_list.php

htdocs/adherents/document.php

htdocs/adherents/subscription/list.php

htdocs/admin/dict.php

htdocs/admin/mails_templates.php

htdocs/admin/tools/listsessions.php

htdocs/admin/websites.php

htdocs/comm/action/listactions.php

htdocs/comm/action/rapport/index.php

htdocs/compta/prelevement/ligne.php

htdocs/fourn/facture/list.php

htdocs/fourn/facture/paiement.php

htdocs/societe/notify/index.php