Fixed printing of LInstructions in the presence of optional arguments

src/arm/lithium-arm.cc

Index: src/arm/lithium-arm.cc
diff --git a/src/arm/lithium-arm.cc b/src/arm/lithium-arm.cc
index fe6a8834d820adaff79df149e3a5ce239c43d5f0..f1947208c5d66f2a4a0d0a4d5002bc3fa15efeed 100644
--- a/src/arm/lithium-arm.cc
+++ b/src/arm/lithium-arm.cc
@@ -112,7 +112,11 @@ void LInstruction::PrintDataTo(StringStream* stream) {
   stream->Add("= ");
   for (int i = 0; i < InputCount(); i++) {
     if (i > 0) stream->Add(" ");
-    InputAt(i)->PrintTo(stream);
+    if (InputAt(i) == NULL) {
+      stream->Add("NULL");
+    } else {
+      InputAt(i)->PrintTo(stream);
+    }
   }
 }