Perhaps you can assign 0 to undefined values. For example with something like this:

  DB<2> $c[$_] = "def" for qw(3 5 6 8 9);

  DB<3> x \@c
0  ARRAY(0x600500c30)
   0  empty slot
   1  empty slot
   2  empty slot
   3  'def'
   4  empty slot
   5  'def'
   6  'def'
   7  empty slot
   8  'def'
   9  'def'
  DB<4>  $c[$_] = $c[$_] // 0 for 0..9;

  DB<5> x \@c
0  ARRAY(0x600500c30)
   0  0
   1  0
   2  0
   3  'def'
   4  0
   5  'def'
   6  'def'
   7  0
   8  'def'
   9  'def'
  DB<6>
[download]