Unmarshal failed to openAI spec

[clockfly]

Describe the bug
Unmarshal yaml failed for https://github.com/openai/openai-openapi/blob/master/openapi.yaml

Error:

oneOf constraint failed for SchemaOrRef with 0 valid results: map[Schema:oneOf constraint failed for SchemaOrRef with 0 valid results: map[Schema:additional properties not allowed in Schema: [$ref] SchemaReference:additional properties not allowed in SchemaReference: [nullable]] SchemaReference:required key missing: $ref]

To Reproduce

yamlFile = "path_to_openapi.yaml"
bytes, _ := ioutil.ReadFile(yamlFile)
spec.UnmarshalYAML(bytes); err != nil {
	fmt.Println(err)
}

Expected behavior
This file should be parsed correctly. This file renders correctly in swagger editor.

https://editor-next.swagger.io/

Additional context
None

[vearutop]

The spec in question is not a valid one.

If you open it in a schema-enabled editor, like the one included in intellij IDEs (e.g. GoLand), you'll see warnings.

The issue here is that OpenAPI 3.0 is based on JSON Schema draft 04, which does not allow any fields adjacent to $ref.
This is also what is told by unmarshal error message (in a cryptic way though):

additional properties not allowed in SchemaReference: [nullable]]

Here are original and fixed schemas:
openai-openapi.json Converted from the YAML original.
openai-openapi-fixed.json Fixed to pass unmarshaling.