Allow optional globals be omitted

src/execution.rs

@@ -68,9 +68,17 @@ impl File {
         for global in &self.globals {
             match globals.get(&global.name) {
                 None => {
-                    if let Some(default) = &global.default {
+                    let default_or_null = global
+                        .default
+                        .as_ref()
+                        .map(|default| default.to_string().into())
+                        .or_else(|| {
+                            (global.quantifier == CaptureQuantifier::ZeroOrOne)
+                                .then_some(Value::Null)
+                        });
+                    if let Some(default_or_null) = default_or_null {
                         globals
-                            .add(global.name.clone(), default.to_string().into())
+                            .add(global.name.clone(), default_or_null)
                             .map_err(|_| {
                                 ExecutionError::DuplicateVariable(format!(
                                     "global variable {} already defined",

tests/it/execution.rs

@@ -290,6 +290,28 @@ fn can_omit_global_variable_with_default() {
     );
 }
 
+#[test]
+fn can_omit_optional_global_variable() {
+    check_execution(
+        "pass",
+        indoc! {r#"
+          global pkgname?
+
+          (module)
+          {
+            node n
+            if (is-null pkgname) {
+              attr (n) pkgname = "fallback"
+            }
+          }
+        "#},
+        indoc! {r#"
+          node 0
+            pkgname: "fallback"
+    "#},
+    );
+}
+
 #[test]
 fn cannot_omit_global_variable() {
     fail_execution(

tests/it/lazy_execution.rs

@@ -291,6 +291,28 @@ fn can_omit_global_variable_with_default() {
     );
 }
 
+#[test]
+fn can_omit_optional_global_variable() {
+    check_execution(
+        "pass",
+        indoc! {r#"
+          global pkgname?
+
+          (module)
+          {
+            node n
+            if (is-null pkgname) {
+              attr (n) pkgname = "fallback"
+            }
+          }
+        "#},
+        indoc! {r#"
+          node 0
+            pkgname: "fallback"
+    "#},
+    );
+}
+
 #[test]
 fn cannot_omit_global_variable() {
     fail_execution(