This has nothing to do with arduino. It's a NullPointerException for a text String.

This will produce the same error:

1. String txt;
2. 
   
3. void setup() {
4.   text(txt, 0, 0);
5. }

The problem is that your text string is null. You should fill it with some text before you display it. Or test if it is null.

1. String txt;
2.  
3. void setup() {
4.   // option 1
5.   if (txt != null) text(txt, 0, 0);
6.  
7.   //option 2
8.   txt = "Some text";
9.   text(txt, 0, 0);
10. }