if($A->b->c != null) //c exists

if(isset($A->b->c)) { // c exists

$identification = $xml->identification;
if (@count($identification->children()) == 0)
  $identification = $xml->Identification;

if( !empty($a->b)){
  var_dump($a->b);
}

if($A->b->c && $A->b->c != '')