generated response schemata have properties with "null" type

I'm using the MockMvc wrapper class. Some of the properties in the response schemata are like
```yaml
networkIp:
description: Network IP
oneOf:
- null
- type: string

```
and the `null` type breaks OAS3 validation. I've tried to address this by specifying the type attribute on the associated test's `responseFields(fieldWithPath("networkIp").description("Network IP").type(JsonFieldType.STRING))`

The detected type is STRING whether or not I add the explicit type attribute to the field.
```bash
❯ jq '.response.responseFields[]|select(.path == "networkIp")' target/generated-snippets/create-ip-host-service/resource.json
{
"attributes": {},
"description": "Network IP",
"ignored": false,
"path": "networkIp",
"type": "STRING",
"optional": false
}
```

...and so I'm looking for validation that the problem must lie within [the Maven plugin generator](https://github.com/BerkleyTechnologyServices/restdocs-spec) that consumes the resource.json snippets in order to produce the OAS3 spec.