[Schema Inefficiency] Lots of code duplication in components that have a `nullable-*` counterpart

[gr2m]

follow up to #543 (review)

Is there any way to remove the duplication between the existing components and their newly introduced nullable-* counterparts?

Example:

      "nullable-license-simple": {
        "title": "License Simple",
        "description": "License Simple",
        "type": "object",
        "properties": {
          "key": { "type": "string", "example": "mit" },
          "name": { "type": "string", "example": "MIT License" },
          "url": {
            "type": "string",
            "nullable": true,
            "format": "uri",
            "example": "https://api.github.com/licenses/mit"
          },
          "spdx_id": { "type": "string", "nullable": true, "example": "MIT" },
          "node_id": { "type": "string", "example": "MDc6TGljZW5zZW1pdA==" },
          "html_url": { "type": "string", "format": "uri" }
        },
        "required": ["key", "name", "url", "spdx_id", "node_id"],
        "nullable": true
      },

and

      "license-simple": {
        "title": "License Simple",
        "description": "License Simple",
        "type": "object",
        "properties": {
          "key": { "type": "string", "example": "mit" },
          "name": { "type": "string", "example": "MIT License" },
          "url": {
            "type": "string",
            "nullable": true,
            "format": "uri",
            "example": "https://api.github.com/licenses/mit"
          },
          "spdx_id": { "type": "string", "nullable": true, "example": "MIT" },
          "node_id": { "type": "string", "example": "MDc6TGljZW5zZW1pdA==" },
          "html_url": { "type": "string", "format": "uri" }
        },
        "required": ["key", "name", "url", "spdx_id", "node_id"]
      },

Is nearly the same, the only diff is

+ "nullable": true

This will generate a ton of unnecessary code down the line.

It's not a critical problem, but I'd appreciate if we could remove the duplication somehow

[xuorig]

Not until we migrate to OpenAPI 3.1 @gr2m. The concept of "nullable references" doesn't work in 3.0 and this is our current workaround. In 3.1 we'll be able to do this:

oneOf:
  - type: null
  - $ref: "user.yaml"