Using Symfony forms without a database entity

Question

I've been developing an application based on Symfony 3, and part of that application involves an import process where a user can upload csv files. One thing that I've never been too sure about with symfony is using the forms component without a database entity to attach it too. In the past I've typically just used an array to hold the form data, but this always felt improper. This time I decided to try building an entity class to base the form on, even though it has no mapping to anything in the database.

This is the entity I created. In addition to defining the fields for the form I also setup validation to ensure at least one of the fields has been populated.

class StudentImportFiles {
    /** @var File */
    private $studentList;
    /** @var File */
    private $transferList;
    /** @var File */
    private $enrollmentList;

    public static function loadValidatorMetadata(ClassMetadata $metadata){
        $metadata->addConstraint(new Callback(function(self $self, ExecutionContextInterface $context){
            if (!($self->studentList || $self->transferList || $self->enrollmentList)){
                $context->addViolation('At least one import file must be selected');
            }
        }));
    }

    public function getStudentList(){
        return $this->studentList;
    }

    public function setStudentList($studentList){
        $this->studentList = $studentList;

        return $this;
    }

    public function getTransferList(){
        return $this->transferList;
    }

    public function setTransferList($transferList){
        $this->transferList = $transferList;

        return $this;
    }

    public function getEnrollmentList(){
        return $this->enrollmentList;
    }

    public function setEnrollmentList($enrollmentList){
        $this->enrollmentList = $enrollmentList;

        return $this;
    }
}

This is the form type I created. It simply maps to the above entity and ensures it is valid.

class StudentImportFilesType extends AbstractType {
    public function buildForm(FormBuilderInterface $builder, array $options){
        $builder
            ->add('studentList', FileType::class, [
                'required' => false
            ])
            ->add('transferList', FileType::class, [
                'required' => false
            ])
            ->add('enrollmentList', FileType::class, [
                'required' => false
            ])
        ;
    }

    public function configureOptions(OptionsResolver $resolver){
        $resolver->setDefaults([
            'data_class' => StudentImportFiles::class
            , 'constraints' => [
                new Valid()
            ]
        ]);
    }
}

Is this proper usage of the forms component for such a scenario? Are there any improvements that could be made?