Empty default values are ignored

[westito]

Empty default values (@Schema(defaultValue = "")) are not included into generated OpenAPI yaml file.

Related code: https://github.com/swagger-api/swagger-core/blob/55ef54df305c2fee98ca58cc91c85183478a9b3a/modules/swagger-core/src/main/java/io/swagger/v3/core/util/AnnotationsUtils.java#L751

Empty values are simply ignored, but many code generation tools are rely on this value. For ex. in Dart generator when no default value provieded, the field became required at code level.

The defaultValue in @Schema annotation should be nullable and passing empty value means include in generated schema.

[juntae6942]

westito I'd like to work on a fix for this. Could you please assign it to me?

[westito]

Feel free to fix