Fix LB failover schemas

LB and amphora failover schemas are explicit null.

Without that generated code fails with `Request must be a JSON dict`.

Change-Id: Ic2a8b46e1c29b0a1e85efe8757d241d3c31b28aa

codegenerator/openapi/octavia.py

@@ -19,6 +19,7 @@ from unittest import mock
 import fixtures
 
 from codegenerator.common.schema import SpecSchema
+from codegenerator.common.schema import TypeSchema
 from codegenerator.openapi.base import (
     OpenStackServerSourceBase,
     _convert_wsme_to_jsonschema,
@@ -1169,3 +1170,34 @@ class OctaviaGenerator(OpenStackServerSourceBase):
             response_body_schema,
             expected_errors,
         )
+
+    def _get_schema_ref(
+        self,
+        openapi_spec,
+        name,
+        description=None,
+        schema_def=None,
+        action_name=None,
+    ):
+        schema: None = None
+        ref: str | None
+        mime_type: str | None = "application/json"
+
+        if name in [
+            "LbaasLoadbalancersFailoverFailoverRequest",
+            "OctaviaAmphoraeFailoverFailoverRequest",
+        ]:
+            schema = openapi_spec.components.schemas.setdefault(
+                name, TypeSchema(type="null")
+            )
+            ref = f"#/components/schemas/{name}"
+        else:
+            (ref, mime_type) = super()._get_schema_ref(
+                openapi_spec,
+                name,
+                description,
+                schema_def=schema_def,
+                action_name=action_name,
+            )
+
+        return (ref, mime_type)