I have a data frame with many features and I know from ad hoc checking that many of them contain the value "NULL" which I would like to replace with NA.

I know that I can use str\_replace column by column, my question is, is there a short hand e.g. 

```
mydf <- mydf %>% str_replace_all("NULL", NA)

```

For example:

```
example_mtcars <- mtcars %>% mutate_at(vars(disp, wt, qsec), funs(as.character(.)))
example_mtcars$disp[c(2,4,8)] <- "NULL"
example_mtcars$wt[c(10, 12)] <- "NULL"
example_mtcars$qsec[c(2,3,4)] <- "NULL"

```

What is the shortest, least code way to replace all instances of "NULL" across the entire data frame example\_mtcars?