82c82
< head->prev = NULL;
---
> head->prev = nullptr;
87c87
< tail->next = NULL;
---
> tail->next = nullptr;
162c162
< return NULL;
---
> return nullptr;
202c202
< blk = NULL;
---
> blk = nullptr;
226c226
< blk = NULL;
---
> blk = nullptr;
280c280
< assert(blk->next == NULL);
---
> assert(blk->next == nullptr);
282c282
< tail->next = NULL;
---
> tail->next = nullptr;
288c288
< blk->prev = NULL;
---
> blk->prev = nullptr;