Fix exception throwing to support no detail message.

(The empty string as a detail message is distinct from a NULL detail message,
and is treated differently by Throwable.printStackTrace.)

Change-Id: I8c65deac9f18c5782dcf6e72e4c37e6dd4174fe9
diff --git a/src/java_lang_reflect_Field.cc b/src/java_lang_reflect_Field.cc
index 185fabc..8e09adb 100644
--- a/src/java_lang_reflect_Field.cc
+++ b/src/java_lang_reflect_Field.cc
@@ -66,7 +66,7 @@
     // Never okay.
     break;
   }
-  Thread::Current()->ThrowNewException("Ljava/lang/IllegalArgumentException;",
+  Thread::Current()->ThrowNewExceptionF("Ljava/lang/IllegalArgumentException;",
       "Not a primitive field: %s", PrettyField(f).c_str());
   return false;
 }
@@ -165,7 +165,7 @@
     // Else fall through to report an error.
   case Class::kPrimVoid:
     // Never okay.
-    Thread::Current()->ThrowNewException("Ljava/lang/IllegalArgumentException;",
+    Thread::Current()->ThrowNewExceptionF("Ljava/lang/IllegalArgumentException;",
         "Not a primitive field: %s", PrettyField(f).c_str());
     return;
   }