OpenAPI schema adding "enum" : [ null ] when field description is added

[cristianonicolai]

Describe the bug

When adding @Schema information to a POJO attribute, the generated schema information on OpenAPI diverges when adding a description. The target description is meant only for the field information and not the type.
For example:

@Schema(nullable = true) RunConfiguration run

Generates:

"run" : {
            "allOf" : [ {
              "$ref" : "#/components/schemas/RunConfiguration"
            } ],
            "nullable" : true
          }

Wheres the same place you add:

@Schema(nullable = true, description = "The run configuration.") RunConfiguration run

Ends up generating:

"run" : {
            "description" : "The run configuration.",
            "type" : "object",
            "anyOf" : [ {
              "$ref" : "#/components/schemas/RunConfiguration"
            }, {
              "enum" : [ null ]
            } ],
            "nullable" : true
          }

Expected behavior

"properties" : {
          "run" : {
           "description" : "The run configuration.",
            "allOf" : [ {
              "$ref" : "#/components/schemas/RunConfiguration"
            } ],
            "nullable" : true
          }
        }

Actual behavior

"properties" : {
          "run" : {
            "description" : "The run configuration.",
            "type" : "object",
            "anyOf" : [ {
              "$ref" : "#/components/schemas/RunConfiguration"
            }, {
              "enum" : [ null ]
            } ],
            "nullable" : true
          }

How to Reproduce?

Created sample project with annotated POJOs here: https://github.com/cristianonicolai/quarkus-playground

Sample annotated field: https://github.com/cristianonicolai/quarkus-playground/blob/main/src/main/java/org/acme/Configuration.java#L7
Generated OpenAPI schema: https://github.com/cristianonicolai/quarkus-playground/blob/main/openapi/openapi.json#L14

Output of uname -a or ver

No response

Output of java -version

No response

Quarkus version or git rev

3.17.7

Build tool (ie. output of mvnw --version or gradlew --version)

Apache Maven 3.9.9

Additional information

No response

[quarkus-bot]

/cc @EricWittmann (openapi), @MikeEdgar (openapi), @phillip-kruger (openapi)

[cristianonicolai]

Possibly related to #45624

[MikeEdgar]

I think this should be fixed with smallrye/smallrye-open-api#2152 and will be included in smallrye-open-api 4.0.7.