fix(bundle): don't look for a $ref pointer on a null value

lib/bundle.ts

@@ -101,8 +101,12 @@ function crawl<S extends object = JSONSchema, O extends ParserOptions<S> = Parse
           crawl(obj, key, keyPath, keyPathFromRoot, indirections, inventory, $refs, options);
         }
 
-        if (value["$ref"]) {
-          bundleOptions?.onBundle?.(value["$ref"], obj[key], obj as any, key);          
+        // We need to ensure that we have an object to work with here because we may be crawling
+        // an `examples` schema and `value` may be nullish.
+        if (value && typeof value === "object" && !Array.isArray(value)) {
+          if ("$ref" in value) {
+            bundleOptions?.onBundle?.(value["$ref"], obj[key], obj as any, key);
+          }
         }
       }
     }

test/specs/bundle-null-value/bundle-null-value-example.yaml

@@ -0,0 +1,12 @@
+defintions:
+  Pet:
+    type: object
+    properties:
+      name:
+        type: string
+      breed:
+        type: string
+        enum: [dog, cat]
+    example:
+      name:
+      breed: dog

test/specs/bundle-null-value/bundle-null-value.spec.ts

@@ -0,0 +1,14 @@
+import { describe, it } from "vitest";
+import { expect } from "vitest";
+import $RefParser from "../../../lib/index.js";
+import path from "../../utils/path";
+import dereferencedSchema from "./bundled";
+
+describe("Bundling schema with nullish values", () => {
+  it("should bundle correctly", async () => {
+    const parser = new $RefParser();
+    const schema = path.rel("test/specs/bundle-null-value/bundle-null-value-example.yaml");
+    const bundled = await parser.bundle(schema);
+    expect(bundled).to.deep.equal(dereferencedSchema);
+  });
+});

test/specs/bundle-null-value/bundled.ts

@@ -0,0 +1,22 @@
+const bundledSchema = {
+  defintions: {
+    Pet: {
+      example: {
+        breed: "dog",
+        name: null,
+      },
+      properties: {
+        breed: {
+          enum: ["dog", "cat"],
+          type: "string",
+        },
+        name: {
+          type: "string",
+        },
+      },
+      type: "object",
+    },
+  },
+};
+
+export default bundledSchema;