xml throwing NullPointer exception

Programmer Question

Can anyone see why the following xml file should throw NullPointer exception?
If I remove all reference to the array hrs_to_wait_values it is ok.
Thanks
Ron

1 hour
2 hours
3 hours
4 hours
5 hours
6 hours
7 hours
8 hours
9 hours
10 hours
11 hours
12 hours
13 hours
14 hours
15 hours
16 hours
17 hours
18 hours
19 hours
20 hours

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

Find the answer here