Fix for annotation SQL update

install/upgrade/text_annotation.sql

@@ -36,7 +36,7 @@ ALTER TABLE model.annotation_text OWNER TO openatlas;
 
 ALTER TABLE ONLY model.annotation_text ADD CONSTRAINT annotation_text_pkey PRIMARY KEY (id);
 CREATE TRIGGER update_modified BEFORE UPDATE ON model.annotation_text FOR EACH ROW EXECUTE FUNCTION model.update_modified();
-ALTER TABLE ONLY model.annotation_text ADD CONSTRAINT annotation_text_entity_id_fkey FOREIGN KEY (entity_id) REFERENCES model.entity(id) ON UPDATE CASCADE ON DELETE CASCADE;
+ALTER TABLE ONLY model.annotation_text ADD CONSTRAINT annotation_text_entity_id_fkey FOREIGN KEY (entity_id) REFERENCES model.entity(id) ON UPDATE CASCADE ON DELETE SET NULL;
 ALTER TABLE ONLY model.annotation_text ADD CONSTRAINT annotation_text_source_id_fkey FOREIGN KEY (source_id) REFERENCES model.entity(id) ON UPDATE CASCADE ON DELETE CASCADE;
 
 END;