To create a simple array or a multidimensional array with defined size and null values​​, use this expression:

<?php

$SimpleArray = array_map(function($n) { return null; }, range(1, 3) );
$MultiArray = array_map(function($n) { return array_map(function($n) { return null; }, range(1, 2) ); }, range(1, 3) );

var_dump($SimpleArray);
var_dump($MultiArray);

// And will print:
?>
>>$SimpleArray
array(3) {
  [0]=>  NULL
  [1]=>  NULL
  [2]=>  NULL
}

>>$MultiArray
array(3) {
  [0]=>  array(2) {
    [0]=>    NULL
    [1]=>    NULL
  }
  [1]=>  array(2) {
    [0]=>    NULL
    [1]=>    NULL
  }
  [2]=>  array(2) {
    [0]=>    NULL
    [1]=>    NULL
  }
}

?>