215             DiffValue::FuncRef { null } => {  in from()
216                 assert!(null);  in from()
219             DiffValue::ExternRef { null } => {  in from()
220                 assert!(null);  in from()
223             DiffValue::AnyRef { null } => {  in from()
224                 assert!(null);  in from()
227             DiffValue::ExnRef { null } => {  in from()
228                 assert!(null);  in from()
231             DiffValue::ContRef { null } => {  in from()
232                 assert!(null);  in from()
247             Val::ExternRef(r) => DiffValue::ExternRef { null: r.is_none() },  in from()
248             Val::FuncRef(r) => DiffValue::FuncRef { null: r.is_none() },  in from()
249             Val::AnyRef(r) => DiffValue::AnyRef { null: r.is_none() },  in from()
250             Val::ExnRef(e) => DiffValue::ExnRef { null: e.is_none() },  in from()
251             Val::ContRef(c) => DiffValue::ContRef { null: c.is_none() },  in from()