gen_hash(codegen_scope *s, node *tree, int val, int limit)
{
  int slimit = GEN_VAL_STACK_MAX;
  if (cursp() >= GEN_LIT_ARY_MAX) slimit = INT16_MAX;
  int len = 0;
  mrb_bool update = FALSE;

  while (tree) {
    if (nint(tree->car->car->car) == NODE_KW_REST_ARGS) {
      if (val && len > 0) {
        pop_n(len*2);
        if (!update) {
          genop_2(s, OP_HASH, cursp(), len);
        }
        else {
          pop();
          genop_2(s, OP_HASHADD, cursp(), len);
        }
        push();
      }
      codegen(s, tree->car->cdr, val);
      if (val && (len > 0 || update)) {
        pop(); pop();
        genop_1(s, OP_HASHCAT, cursp());
        push();
      }
      update = TRUE;
      len = 0;
    }
    else {
      codegen(s, tree->car->car, val);
      codegen(s, tree->car->cdr, val);
      len++;
    }
    tree = tree->cdr;
    if (val && cursp() >= slimit) {
      pop_n(len*2);
      if (!update) {
        genop_2(s, OP_HASH, cursp(), len);
      }
      else {
        pop();
        genop_2(s, OP_HASHADD, cursp(), len);
      }
      push();
      update = TRUE;
      len = 0;
    }
  }
  if (update) {
    if (val && len > 0) {
      pop_n(len*2+1);
      genop_2(s, OP_HASHADD, cursp(), len);
      push();
    }
    return -1;                  /* variable length */
  }
  return len;
}
A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.