chore: Use null instead of undefined.

Author: gonfunko

src/navigation.ts

@@ -239,9 +239,9 @@ export class Navigation {
     if (!e.workspaceId) {
       return;
     }
-    const flyoutWorkspace = Blockly.Workspace.getById(e.workspaceId) as
-      | Blockly.WorkspaceSvg
-      | undefined;
+    const flyoutWorkspace = Blockly.Workspace.getById(
+      e.workspaceId,
+    ) as Blockly.WorkspaceSvg | null;
     const mainWorkspace = flyoutWorkspace?.targetWorkspace;
     if (!mainWorkspace) {
       return;