Due to the removal of nullable: true from schema in 3.1.0, it appears that the nullable = true property on the @Schema annotation no longer works. That isn't obvious in the documentation for the annotation, and it's inconvenient to boot ;-)

I think it will be quite easy to continue to support the nullable attribute under 3.1.0, I suggest a little change to Schema.getTypes:

    @OpenAPI31
    public Set<String> getTypes() {
        if (types != null) {
            if (nullable != null && nullable.booleanValue()) {
                Set<String> ss = new LinkedHashSet<>(types);
                ss.add("null");
                return ss;
            } else {
                return types;
            }
        } else {
            return null;
        }
    }

We simply add "null" to the list of types if the schema is nullable... which ends up nicely in the schema output.

I'm happy to make a PR of this, or a better suggestion, or I'd love to know if this is more like the wrong approach!