In my simulation I need a vector that looks like:

```
vec = NULL NULL NULL NULL 2 2 2 2 4 4 4 4

```

However, in R when I use `rep(NULL, 4)` it returns nothing. For example,

```
vec.all = c(rep(NULL, 4), rep(2, 4), rep(4, 4))
vec.all
2 2 2 2 4 4 4 4

```

Is there a way to repeat `NULL` several times in R? Thanks!