Any? is generated with type of null in 3.0.3

[petergphillips]

Describe the bug
After the upgrade from springdoc 3.0.2 to 3.0.3 we've noticed that

  val anyName: Any? = null,

gets generated as

          "anyName" : {
            "type" : "null"
          }

This causes problems with the openapi generator as it then thinks that the type can only be null and tries to generate a Null type etc.

Under springdoc 3.0.2 the same code generated:

          "anyName" : { }

To Reproduce

• What version of spring-boot you are using? 4.0.5
• What version of kotlin are you using? 2.3.20
• What modules and versions of springdoc-openapi are you using? 3.0.3
• What is the actual and the expected result using OpenAPI Description (yml or json)? See above for actual and also the generated code in 3.0.2. I would expect the type not to just be "null".
• Provide with a sample code (HelloController) or Test that reproduces the problem

@RestController
class IssuesController {
  @GetMapping("/")
  fun greet(greeting: Greeting): String = greeting.anyName?.toString() ?: "Hello World"
}

data class Greeting(
  val anyName: Any? = null,
)

Expected behavior
Note that if the field is defined as

  val stringName: String? = null,

then the generated code is

            "type" : [ "string", "null" ]

I think it is therefore because Any doesn't have a type and therefore null just gets inserted instead. I guess one option is to remove the null if it is the only type found?

Additional context
Looks to be a side effect of #3256.

[petergphillips]

See https://github.com/petergphillips/springdoc-issues/blob/pgp-springdoc-3273/README.md for a sample project and test demonstrating the issue.

[rupert-jung-mw]

Happed for me also and broke my typescript frontend on dozends of places.

How can I restore the original behavior? Isn't there a config key for that? The type should just stay "string" (and not listed as "required")? Any why is such a critical change added to a patch release (x.x.3) ?

[petergphillips]

Note that I'm perfectly happy with the generation of

            "type" : [ "string", "null" ]

for String? fields. My issue is the with the generation of

            "type" : "null"

for Any? fields as the type is then just null and doesn't have a oneOf or anything else.

If you're not happy with that behaviour (which I think is part of the 3.1 specification) then one option is to switch to OpenApi 3.0 generation i.e. setting:

springdoc.api-docs.version: openapi_3_0

in your application.yaml.

[rupert-jung-mw]

FYI: This is likely to be reverted in the next version:
#3276 (comment)

For the future I would highly appreciate to release a new minor version (0.x) for changes like this instead of a patch version (0.0.x) as this is deliberately changing the behavior.