diff -r eecf6077ec4e -r 1ff540c1650f vm/src/main/java/org/apidesign/vm4brwsr/ByteCodeToJavaScript.java
--- a/vm/src/main/java/org/apidesign/vm4brwsr/ByteCodeToJavaScript.java	Tue Feb 05 16:40:01 2013 +0100
+++ b/vm/src/main/java/org/apidesign/vm4brwsr/ByteCodeToJavaScript.java	Tue Feb 05 17:04:22 2013 +0100
@@ -1278,7 +1278,7 @@
                     int indx = readIntArg(byteCodes, i);
                     final String type = jc.getClassName(indx);
                     if (!type.startsWith("[")) {
-                        emit(out, "var @2 = @1.$instOf_@3 ? 1 : 0;",
+                        emit(out, "var @2 = @1 != null && @1.$instOf_@3 ? 1 : 0;",
                              smapper.popA(), smapper.pushI(),
                              type.replace('/', '_'));
                     } else {