fix: avoid crashing in the no-required-schema-properties-undefined rule when encountering unresolved $ref (#2413)

Co-authored-by: ryo_sakurai <ryo_sakurai@mates-system.com>

Author: sakurai-ryo

.changeset/rotten-llamas-knock.md

@@ -0,0 +1,6 @@
+---
+"@redocly/openapi-core": patch
+"@redocly/cli": patch
+---
+
+Fixed an issue where the `no-required-schema-properties-undefined` caused a crash when encountering unresolved `$ref`s.

packages/core/src/rules/common/__tests__/no-required-schema-properties-undefined.test.ts

@@ -944,4 +944,44 @@ describe('no-required-schema-properties-undefined', () => {
       ]
     `);
   });
+
+  it('should not crash on unresolved $ref', async () => {
+    const document = parseYamlToDocument(
+      outdent`
+          openapi: 3.0.0
+          components:
+            schemas:
+              Object:
+                allOf:
+                  - $ref: '#/components/schemas/NotExists'
+                required:
+                  - name
+        `,
+      'foobar.yaml'
+    );
+
+    const results = await lintDocument({
+      externalRefResolver: new BaseResolver(),
+      document,
+      config: await createConfig({ rules: { 'no-required-schema-properties-undefined': 'error' } }),
+    });
+
+    expect(replaceSourceWithRef(results)).toMatchInlineSnapshot(`
+      [
+        {
+          "location": [
+            {
+              "pointer": "#/components/schemas/Object/required/0",
+              "reportOnKey": false,
+              "source": "foobar.yaml",
+            },
+          ],
+          "message": "Required property 'name' is undefined.",
+          "ruleId": "no-required-schema-properties-undefined",
+          "severity": "error",
+          "suggest": [],
+        },
+      ]
+    `);
+  });
 });

packages/core/src/rules/common/no-required-schema-properties-undefined.ts

@@ -38,10 +38,10 @@ export const NoRequiredSchemaPropertiesUndefined:
 
           if (isRef(schema)) {
             const resolved = resolve<AnySchema>(schema, from);
-            return elevateProperties(
-              resolved.node as AnySchema,
-              resolved.location?.source.absoluteRef
-            );
+            if (!resolved.node) {
+              return {};
+            }
+            return elevateProperties(resolved.node, resolved.location?.source.absoluteRef);
           }
 
           return Object.assign(