Based on the provided code slice and the identified vulnerability (CWE-476: NULL Pointer Dereference) on line 16, here are five possible patches to address the issue:

Patch 1:
```c
16 		map = READ_ONCE(ri->map);
17 		if (!map) {
18 			err = -EINVAL;
19 			goto err;
20 		}
```

Patch 2:
```c
16 		map = READ_ONCE(ri->map);
17 		if (unlikely(!map)) {
18 			pr_err("NULL map pointer encountered\n");
19 			return -EFAULT;
20 		}
```

Patch 3:
```c
15 	case BPF_MAP_TYPE_DEVMAP_HASH:
16 		map = READ_ONCE(ri->map);
17 		if (IS_ERR_OR_NULL(map)) {
18 			err = PTR_ERR(map) ?: -EINVAL;
19 			goto err;
20 		}
```

Patch 4:
```c
16 		map = READ_ONCE(ri->map);
17 		if (!map) {
18 			dev_warn(dev, "Null map pointer in xdp_do_generic_redirect_map\n");
19 			return -ENOENT;
20 		}
```

Patch 5:
```c
15 	case BPF_MAP_TYPE_DEVMAP_HASH: {
16 		struct bpf_map *tmp_map = READ_ONCE(ri->map);
17 		if (!tmp_map) {
18 			err = -EFAULT;
19 			goto err;
20 		}
21 		map = tmp_map;
```