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/reference_table_test.cc b/runtime/reference_table_test.cc
index db98e1f..4ffebf2 100644
--- a/runtime/reference_table_test.cc
+++ b/runtime/reference_table_test.cc
@@ -40,8 +40,8 @@
     EXPECT_EQ(0U, rt.Size());
   }
 
-  // Check removal of all NULLs in a empty table is a no-op.
-  rt.Remove(NULL);
+  // Check removal of all nullss in a empty table is a no-op.
+  rt.Remove(nullptr);
   EXPECT_EQ(0U, rt.Size());
 
   // Check removal of all o1 in a empty table is a no-op.