feat: Display nullable for object model itself (#5660) (#5868)

test/e2e-cypress/static/documents/bugs/5660-model.yaml

@@ -0,0 +1,14 @@
+openapi: 3.0.2
+info:
+  title: test
+  description: Nullable model itself
+  version: '1.0'
+paths: {}
+components:
+  schemas:
+    SomeObject:
+      type: object
+      properties:
+        name:
+          type: string
+      nullable: true

test/e2e-cypress/static/documents/bugs/5660-property.yaml

@@ -0,0 +1,17 @@
+openapi: 3.0.2
+info:
+  title: test
+  description: Nullable object in model property
+  version: '1.0'
+paths: {}
+components:
+  schemas:
+    SomeObject:
+      type: object
+      properties:
+        meta:
+          type: object
+          properties:
+            tag:
+              type:  string
+          nullable: true