**Found in version**
- Observed in 8.2.3, but might exist longer

**Steps to reproduce**
On a multi node cloud cluster (might also work on a local multi node cluster):
- Create a transform with a retention policy
- Update the transform and remove the retention policy

**Expected result**
- The retention policy is removed

**Actual result**
- This sometimes results in an error:
```
An error occurred calling the API endpoint to update transforms.
Bad Request: [illegal_argument_exception: [illegal_argument_exception] Reason: 
Unknown NamedWriteable [org.elasticsearch.xpack.core.transform.transforms.RetentionPolicyConfig][null_retention_policy]]:
Unknown NamedWriteable [org.elasticsearch.xpack.core.transform.transforms.RetentionPolicyConfig][null_retention_policy]
```

**Additional information**
- Quote from slack discussion with @benwtrent:
  > It wouldn’t happen if you hit a node that can execute the update immediately without serializing to a different node
x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/transform/transforms/NullRetentionPolicyConfig.java
public static final ParseField NAME = new ParseField("null_retention_policy");
    public static final NullRetentionPolicyConfig INSTANCE = new NullRetentionPolicyConfig();
    private NullRetentionPolicyConfig() {}
    @Override
    public ActionRequestValidationException validate(ActionRequestValidationException validationException) {
        throw new UnsupportedOperationException();
    }
    @Override
    public void checkForDeprecations(String id, NamedXContentRegistry namedXContentRegistry, Consumer<DeprecationIssue> onDeprecation) {
        throw new UnsupportedOperationException();
    }
    @Override
    public XContentBuilder toXContent(final XContentBuilder builder, final Params params) throws IOException {
        throw new UnsupportedOperationException();
    }
    @Override
    public String getWriteableName() {
        return NAME.getPreferredName();
    }
    @Override
    public void writeTo(final StreamOutput out) throws IOException {}
}