Replace NULL with nullptr

Also fixed some lines that were too long, and a few other minor
details.

Change-Id: I6efba5fb6e03eb5d0a300fddb2a75bf8e2f175cb
diff --git a/runtime/exception_test.cc b/runtime/exception_test.cc
index 1770658..6808000 100644
--- a/runtime/exception_test.cc
+++ b/runtime/exception_test.cc
@@ -200,7 +200,7 @@
   fake_stack.push_back(0);
   fake_stack.push_back(0xEBAD6070);  // return pc
 
-  // Push Method* of NULL to terminate the trace
+  // Push Method* of null to terminate the trace
   fake_stack.push_back(0);
 
   // Push null values which will become null incoming arguments.