mrb_singleton_class_ptr(mrb_state *mrb, mrb_value v)
{
  struct RBasic *obj;

  switch (mrb_type(v)) {
  case MRB_TT_FALSE:
    if (mrb_nil_p(v))
      return mrb->nil_class;
    return mrb->false_class;
  case MRB_TT_TRUE:
    return mrb->true_class;
  case MRB_TT_CPTR:
  case MRB_TT_SYMBOL:
  case MRB_TT_INTEGER:
#ifndef MRB_NO_FLOAT
  case MRB_TT_FLOAT:
#endif
    return NULL;
  default:
    break;
  }
  obj = mrb_basic_ptr(v);
  if (obj->c == NULL) return NULL;
  prepare_singleton_class(mrb, obj);
  return obj->c;
}
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.