I found issues with '\Symfony\Component\Validator\Constraints\NotBlank'. When merged fix for this bug #2222 can't set the property required if it has default value.

In my opinion, the current behavior is correct and works as intended.

Consider a scenario where the DTO is used not for a GET endpoint but for a POST or PUT API endpoint by your Angular application - the proposed changes in #2288 would create an inconsistency (which got caught by a failing test): When your Angular app sends data, it would be correct that $count is not marked as required, as the data and the DTO would still be valid even if the $count property wasn't included (since there is a fallback/default value). This means it is, in fact, an optional value.

This logic applies to your case as well, and I don't believe there is an easy solution within the Nelmio bundle. However, a simple fix for your problem could be to avoid defining the default value at the property level. Instead, you can define it within the getCount() method, as shown below (additionally, see https://3v4l.org/YlcuX):

class GetContactDto
{
    protected int $count;

    public function getCount(): int
    {
        return $this->count ?? 0;
    }
}

I think a way we could "fix" this is by introducing some kind of new attribute to make it a little bit easier for users to mark their property as required=true|false. This could then be done on the property level instead of on class level.

class GetContactsDto
{
    /**
     * @var Contact[]
     */
    #[Required]
    protected array $items = [];

Using the solution provided by @DominicLuidold seems a little bit hacky for this, but for now you should be able to overwrite the setting it as required with the OA\Schema attribute from swagger-php.

#[OA\Schema(required: ['items'])]
class GetContactsDto
{
...

I think a way we could "fix" this is by introducing some kind of new attribute to make it a little bit easier for users to mark their property as required=true|false. This could then be done on the property level instead of on class level.

class GetContactsDto
{
    /**
     * @var Contact[]
     */
    #[Required]
    protected array $items = [];

Using the solution provided by @DominicLuidold seems a little bit hacky for this, but for now you should be able to overwrite the setting it as required with the OA\Schema attribute from swagger-php.

#[OA\Schema(required: ['items'])]
class GetContactsDto
{
...

I think this would be great. There is still a lot of confusion about required and optional parameters in the resulting schema. More so, if the attribute can be nullable. Or when the attribute can be undefined but when it is, it has to be non-nullable.