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/arch/mips/context_mips.h b/runtime/arch/mips/context_mips.h
index cbad3f963..d01b95e 100644
--- a/runtime/arch/mips/context_mips.h
+++ b/runtime/arch/mips/context_mips.h
@@ -79,7 +79,7 @@
   NO_RETURN void DoLongJump() OVERRIDE;
 
  private:
-  // Pointers to registers in the stack, initialized to NULL except for the special cases below.
+  // Pointers to registers in the stack, initialized to null except for the special cases below.
   uintptr_t* gprs_[kNumberOfCoreRegisters];
   uint32_t* fprs_[kNumberOfFRegisters];
   // Hold values for sp and ra (return address) if they are not located within a stack frame.