determining if array element is null

[eastanon via Digitalmars-d-learn]

Does D array implementation support an array of null values?
int a[4] = null;

But I ran into a type error while checking if a[i] is null

foreach(i; 0..3){
 if(i == null){
   writeln("it is null");
   }
  }
}

How do you set fixed size array of null values and check if they 
are null?