Fix student publication migration see BT#15056

app/Migrations/Schema/V111/Version20160715122300.php

@@ -23,7 +23,7 @@ class Version20160715122300 extends AbstractMigrationChamilo
         $this->addSql('ALTER TABLE c_student_publication CHANGE session_id session_id INT DEFAULT NULL');
         $this->addSql('UPDATE c_student_publication SET session_id = NULL WHERE session_id = 0');
         // Fix not existing session id
-        $this->addSql('DELETE FROM c_student_publication WHERE session_id not in (SELECT id FROM session)');
+        $this->addSql('DELETE FROM c_student_publication WHERE session_id <> NULL AND session_id not in (SELECT id FROM session)');
         $this->addSql('ALTER TABLE c_student_publication ADD CONSTRAINT fk_session FOREIGN KEY (session_id) REFERENCES session (id)');
     }