Virtual Chassis master field cannot be null according to the API
### NetBox version

v3.2.9

### Python version

3.10

### Steps to Reproduce

1. Submit API write request to the VirtualChassis with "master": null in it

### Expected Behavior

Requests is accepted and the master is unset for the specific VirtualChassis

### Observed Behavior

HTTP 400 is returned with the message: `[{"master":["This field may not be null."]}]`
diff --git a/netbox/dcim/api/serializers.py b/netbox/dcim/api/serializers.py
index 79f5339ad..897ee4ca3 100644
--- a/netbox/dcim/api/serializers.py
+++ b/netbox/dcim/api/serializers.py
@@ -1076,7 +1076,7 @@ class CablePathSerializer(serializers.ModelSerializer):
 
 class VirtualChassisSerializer(NetBoxModelSerializer):
     url = serializers.HyperlinkedIdentityField(view_name='dcim-api:virtualchassis-detail')
-    master = NestedDeviceSerializer(required=False)
+    master = NestedDeviceSerializer(required=False, allow_null=True, default=None)
     member_count = serializers.IntegerField(read_only=True)
 
     class Meta:
diff --git a/netbox/dcim/tests/test_api.py b/netbox/dcim/tests/test_api.py
index acd52178d..2697c29b2 100644
--- a/netbox/dcim/tests/test_api.py
+++ b/netbox/dcim/tests/test_api.py
@@ -2057,6 +2057,7 @@ class VirtualChassisTest(APIViewTestCases.APIViewTestCase):
 
         cls.bulk_update_data = {
             'domain': 'newdomain',
+            'master': None
         }
 
 
['netbox/dcim/tests/test_api.py', 'netbox/dcim/api/serializers.py']