How to UPDATE a column to SET previous row value to NULL cells?

Question

I have a table as

id  value
1   music
2 
3   movie
4   
5
6   book
7
8

Some values are missing, and I want to assign the value of previous row to produce

id  value
1   music
2   music
3   movie
4   movie
5   movie
6   book
7   book
8   book