diff -r df84c02f4780 -r 6372f5af9612 src/hotspot/share/jfr/dcmd/jfrDcmds.cpp
--- a/src/hotspot/share/jfr/dcmd/jfrDcmds.cpp	Mon Nov 05 14:02:04 2018 +0100
+++ b/src/hotspot/share/jfr/dcmd/jfrDcmds.cpp	Mon Nov 05 14:40:16 2018 +0100
@@ -446,6 +446,12 @@
       assert(element != NULL, "invariant");
       JfrJavaSupport::set_array_element(settings, element, i, CHECK);
     }
+  } else {
+    settings = JfrJavaSupport::new_string_array(1, CHECK);
+    assert(settings != NULL, "invariant");
+    jobject element = JfrJavaSupport::new_string("default", CHECK);
+    assert(element != NULL, "invariant");
+    JfrJavaSupport::set_array_element(settings, element, 0, CHECK);
   }
 
   static const char klass[] = "jdk/jfr/internal/dcmd/DCmdStart";