Adapted some typing requirements

Author: MarcoMuellner

noxfile.py

@@ -23,7 +23,7 @@
 
 
 package = "openapi_python_generator"
-python_versions = ["3.10", "3.9", "3.8", "3.7"]
+python_versions = ["3.9", "3.8"]
 nox.needs_version = ">= 2021.6.6"
 nox.options.sessions = (
     "pre-commit",

src/openapi_python_generator/language_converters/python/model_generator.py

@@ -60,7 +60,7 @@ def _generate_property_from_schema(name: str, schema: Schema, parentSchema: Opti
     :param parentSchema: Component this belongs to
     :return: Property
     """
-    required = parentSchema.required is not None and name in parentSchema.required
+    required = parentSchema is not None and parentSchema.required is not None and name in parentSchema.required
     return Property(
         name=name,
         type=type_converter(schema, required),