Adds spec additionalProperties + nullable examples (#2405)

* Adds v2 spec additionalproperties examples, adds v3 spec nulllable model example, updates samples

* Remaining samples updates

* Adds csharp generator update to handle models with multilevel parent types, which works for the AdditionalPropertiesObject model, samples updated

samples/openapi3/client/petstore/python/test/test_nullable_class.py

@@ -0,0 +1,39 @@
+# coding: utf-8
+
+"""
+    OpenAPI Petstore
+
+    This spec is mainly for testing Petstore server and contains fake endpoints, models. Please do not use this for any other purpose. Special characters: \" \\  # noqa: E501
+
+    OpenAPI spec version: 1.0.0
+    Generated by: https://openapi-generator.tech
+"""
+
+
+from __future__ import absolute_import
+
+import unittest
+
+import petstore_api
+from petstore_api.models.nullable_class import NullableClass  # noqa: E501
+from petstore_api.rest import ApiException
+
+
+class TestNullableClass(unittest.TestCase):
+    """NullableClass unit test stubs"""
+
+    def setUp(self):
+        pass
+
+    def tearDown(self):
+        pass
+
+    def testNullableClass(self):
+        """Test NullableClass"""
+        # FIXME: construct object with mandatory attributes with example values
+        # model = petstore_api.models.nullable_class.NullableClass()  # noqa: E501
+        pass
+
+
+if __name__ == '__main__':
+    unittest.main()