DatabaseCondition::isNull in core/includes/database/query.inc

Sets a condition that the specified field be NULL.

DeleteQuery::isNull in core/includes/database/query.inc

MergeQuery::isNull in core/includes/database/query.inc

Sets a condition that the specified field be NULL.

SelectQuery::isNull in core/includes/database/select.inc

SelectQueryExtender::isNull in core/includes/database/select.inc

Sets a condition that the specified field be NULL.

UpdateQuery::isNull in core/includes/database/query.inc