optional() is not working in OpenAPI 3

First of all thank you very much for your contribution on rest docs.

Here is my debug screenshot

and section of `resource.json`

```json
"requestFields" : [{
"attributes" : { },
"description" : "",
"ignored" : false,
"path" : "nickname",
"type" : "STRING",
"optional" : false
}, {
"attributes" : { },
"description" : "",
"ignored" : false,
"path" : "avatar",
"type" : "STRING",
"optional" : true
}, {
"attributes" : { },
"description" : "",
"ignored" : false,
"path" : "gender",
"type" : "NUMBER",
"optional" : true
} ]
```

and section of `openapi3.yaml`

```yaml
UserSignUpMessage:
title: UserSignUpMessage
type: object
properties:
gender: {type: number, description:}
avatar: {type: string, description: }
nickname: {type: string, description:}
```

Each section is relatively complete, I have read #90 #172 that It doesn't seem to help me much. I'm not sure if I'm missing something, or doing something stupid

:)