Replace NULL with nullptr

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

Change-Id: I6efba5fb6e03eb5d0a300fddb2a75bf8e2f175cb
diff --git a/compiler/dex/mir_graph.h b/compiler/dex/mir_graph.h
index d7e4dd9..0db54bf 100644
--- a/compiler/dex/mir_graph.h
+++ b/compiler/dex/mir_graph.h
@@ -602,7 +602,7 @@
 
   BasicBlock* GetBasicBlock(unsigned int block_id) const {
     DCHECK_LT(block_id, block_list_.size());  // NOTE: NullBasicBlockId is 0.
-    return (block_id == NullBasicBlockId) ? NULL : block_list_[block_id];
+    return (block_id == NullBasicBlockId) ? nullptr : block_list_[block_id];
   }
 
   size_t GetBasicBlockListCount() const {