fixup! stack-switching: add stub Val::ContRef

Author: posborne

crates/wasmtime/src/runtime/externals/global.rs

@@ -276,7 +276,7 @@ impl Global {
                 }
                 Val::ContRef(None) => {
                     // Allow null continuation references for globals - these are just placeholders
-                    // Non-null references are not supported yet
+                    definition.write_gc_ref(&mut store, None);
                 }
                 Val::ContRef(Some(_)) => {
                     // TODO(#10248): Implement non-null global continuation reference handling

crates/wasmtime/src/runtime/trampoline/global.rs

@@ -72,7 +72,7 @@ pub fn generate_global_export(
             }
             Val::ContRef(None) => {
                 // Allow null continuation references for trampoline globals - these are just placeholders
-                // Non-null references are not supported yet
+                global.write_gc_ref(&mut store, None);
             }
             Val::ContRef(Some(_)) => {
                 // TODO(#10248): Implement non-null trampoline continuation reference handling