Symfony 4 handling null DateType form field

You should allow put null in method setDateOfBirth. The correct version:

public function setDateOfBirth(?\DateTimeInterface $DateOfBirth): self
{
    $this->DateOfBirth = $DateOfBirth;

    return $this;
}

Because entity is populated values from request by setters before validating

Use the empty_data option to do this.

$builder
     ->add('someDate', \Symfony\Component\Form\Extension\Core\Type\DateType::class, [
        'widget' => 'single_text',
        'required' => false,
        'empty_data' => '',
     ])
;

The default value of by_reference option in DateType, DateTimeType and TimeType is false.

So in here $this->propertyAccessor->setValue($data, $propertyPath, $propertyValue); is called and here {An instance of PatientSearch}->setDateOfBirth(null) is called.

But argument for setDateOfBirth(\DateTimeInterface $DateOfBirth) is not nullable. So you get that error.

You can prevent the error with making argument nullable like this:

public function setDateOfBirth(?\DateTimeInterface $DateOfBirth): self
{
    $this->DateOfBirth = $DateOfBirth;

    return $this;
}

or turning by_reference true like this:

->add('DateOfBirth', DateType::class, array(
    'required' => false,
    'widget' => 'single_text',
    'by_reference' => true,
))

I wound up just using a TextType to do this as it was easier and there didn't seem to be a solution with using a DateType. In fact it looks like this is a issue being reviewed on the Symfony github issues (ticket here) as the DateTimeType/DateType doesn't seem to work properly with the empty_data attribute.

The trick here is when you get the field it is a date type, but when you set it the type is a string which attempts to convert to datetime and if it fails then the field is just not set. The field itself is still a date data type.

Type file

->add('DateOfBirth', TextType::class, array(
    'required' => false,
    'empty_data' => null,
    'attr' => array(
        'placeholder' => 'mm/dd/yyyy'
    )))

Twig file

{{ form_widget(search_form.DateOfBirth) }}

Entity file

/**
 * @ORM\Column(type="date", nullable=true)
 */
private $DateOfBirth;

...

public function getDateOfBirth(): ?\DateTimeInterface
{
    return $this->DateOfBirth;
}

public function setDateOfBirth(string $DateOfBirth): self
{
    try {

        $this->DateOfBirth = new \DateTime($DateOfBirth);
    }
    catch(\Exception $e) {
       //Do Nothing
    }

    return $this;
}