Filtering data in R

Question

I have a CSV of file of data that I can load in R using read.csv()

Some of the data is missing, so I want to reduce the data frame down to set that consists entirely of non-missing data, i.e. if a NULL appears anywhere, I want to exclude that column and row from the filtered data set.

I know I can probably do this fairly simply with the inbuilt R vector operations, but I am not quite sure how to do this exactly?

To make my question a little more concrete, here is a quick sample of the data so you can see what I want to do.

DocID       Anno1    Anno7  Anno8
1           7        NULL   8
2           8        NULL   3
44          10       2      3
45          6        6      6
46          1        3      4
49          3        8      5
62          4        NULL   9
63          2        NULL   4
67          11       NULL   3
91          NULL     9      7
92          NULL     7      5
93          NULL     8      8

So given this input, I need some code that will reduce the output to this.

DocID       Anno8
44          3
45          6
46          4
49          5

As Anno8 is the only column with non-NULL data, and there are only four rows with non-NULL data.