get default string value

[buddhi mihara]

i registered a custom object call process using java(class extends from ScriptObject class).but when i do following it throws an exceptions
var obj =  {foo:23};Object.bindProperties(process,obj) 
Exception in thread "main" ECMAScript Exception: TypeError: Cannot get default string value	at jdk.nashorn.internal.runtime.ECMAErrors.error(ECMAErrors.java:57)	at jdk.nashorn.internal.runtime.ECMAErrors.typeError(ECMAErrors.java:213)	at jdk.nashorn.internal.runtime.ECMAErrors.typeError(ECMAErrors.java:185)	at jdk.nashorn.internal.objects.Global.getDefaultValue(Global.java:571)	at jdk.nashorn.internal.runtime.ScriptObject.getDefaultValue(ScriptObject.java:1257)	at jdk.nashorn.internal.runtime.JSType.toPrimitive(JSType.java:264)	at jdk.nashorn.internal.runtime.JSType.toStringImpl(JSType.java:901)	at jdk.nashorn.internal.runtime.JSType.toString(JSType.java:323)	at jdk.nashorn.tools.Shell.readEvalPrint(Shell.java:450)	at jdk.nashorn.tools.Shell.run(Shell.java:162)	at jdk.nashorn.tools.Shell.main(Shell.java:134)	at jdk.nashorn.tools.Shell.main(Shell.java:113)
solution please