OptString.Decode() fails on JSON null values

[BrandtKruger]

Description

The generated OptString.Decode() method in oas_json_gen.go fails when encountering null values in JSON,
causing errors like "unexpected byte 110 'n'".

Expected Behavior

OptString should handle null values gracefully, similar to how OptNilString handles them.

Current Behavior

func (o *OptString) Decode(d *jx.Decoder) error {
    o.Set = true
    v, err := d.Str()  // Fails on null
    if err != nil {
        return err
    }
    o.Value = string(v)
    return nil
}



Suggested Fix

func (o *OptString) Decode(d *jx.Decoder) error {
    if d.Next() == jx.Null {
        if err := d.Null(); err != nil {
            return err
        }
        o.Set = false
        o.Value = ""
        return nil
    }
    o.Set = true
    v, err := d.Str()
    if err != nil {
        return err
    }
    o.Value = string(v)
    return nil
}