Fixed printing of LInstructions in the presence of optional arguments

src/mips/lithium-mips.cc

Index: src/mips/lithium-mips.cc
diff --git a/src/mips/lithium-mips.cc b/src/mips/lithium-mips.cc
index 521b38d0cd04a0a57b0d4586699f08327710c2e7..0e58eb55104ae3abe77bf53c9a427eda36a1b901 100644
--- a/src/mips/lithium-mips.cc
+++ b/src/mips/lithium-mips.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);
+    }
   }
 }