Inserting a blank row to every other row

Starting from this data frame:

my.df <- data.frame(num = 1:5, let = letters[1:5])

my.df

num let
1   1   a
2   2   b
3   3   c
4   4   d
5   5   e

and inserting a blank row (NAs row) for each one of my.df rows.

na.df <- data.frame(num = NA, let = NA)

my.df <- do.call(rbind, apply(my.df, 1, function(x) {rbind(x, na.df)}))

my.df

num  let
1     1    a
2  <NA> <NA>
3     2    b
4  <NA> <NA>
5     3    c
6  <NA> <NA>
7     4    d
8  <NA> <NA>
9     5    e
10 <NA> <NA>

--

Best,

GG