symfony 3.4 Type error: Argument 1 passed to … must be an instance of DateTime, null given,

问题

In the entity the date time is decalared:

 /**
 * @var \DateTime
 * @ORM\Column(name="task_date_start", type="datetime", nullable=true)
 */
 private $taskDateStart;

in the form

$builder->add('taskDateStart', DateType::class, [
    "widget" => "single_text",
    "html5" => false,
    "format" => "dd-MM-yyyy"  ,
    "attr" => ["class" => "js-datepicker"], 
    "required" => false                                                    
]);

i've this error when inserting null in to the field

Argument 1 passed to ... must be an instance of DateTime, null given

回答1:

The problem was solved by modifying the setter (new setter without prototype):

 function setTaskDateStart(\DateTime $taskDateStart = null ) {
     $this->taskDateStart = $taskDateStart;
 }

become

 function setTaskDateStart( $taskDateStart ) {
     $this->taskDateStart = $taskDateStart;
 }

回答2:

Better solution is to allow set the null and let the validation reports the error.

/**
 * @var \DateTime
 * @ORM\Column(name="task_date_start", type="datetime", nullable=false)
 * @Assert\NotBlank()
 */
 private $taskDateStart;

and

 function setTaskDateStart(?\DateTime $taskDateStart) {
     $this->taskDateStart = $taskDateStart;
 }

来源：https://stackoverflow.com/questions/48826086/symfony-3-4-type-error-argument-1-passed-to-must-be-an-instance-of-datetime