Site: Removing timezone fails via api because time_zone does not allow nulls

[amhn]

NetBox version

v3.3.6 & master

Python version

3.10

Steps to Reproduce

1. Create site with time_zone, e.g. Europe/Berline
2. Send {"time_zone": null} to /api/dcim/site// method PATCH

Expected Behavior

Time zone is unset.

Observed Behavior

An error is returned:

{"time_zone":["This field may not be null."]}

[amhn]

Fixed with:

diff --git a/netbox/dcim/api/serializers.py b/netbox/dcim/api/serializers.py
index 897ee4ca3..cb1edfe1f 100644
--- a/netbox/dcim/api/serializers.py
+++ b/netbox/dcim/api/serializers.py
@@ -130,7 +130,7 @@ class SiteSerializer(NetBoxModelSerializer):
     region = NestedRegionSerializer(required=False, allow_null=True)
     group = NestedSiteGroupSerializer(required=False, allow_null=True)
     tenant = NestedTenantSerializer(required=False, allow_null=True)
-    time_zone = TimeZoneSerializerField(required=False)
+    time_zone = TimeZoneSerializerField(required=False, allow_null=True)
     asns = SerializedPKRelatedField(
         queryset=ASN.objects.all(),
         serializer=NestedASNSerializer,

See also #10791

[jeremystretch]

Thanks!