FULL PRODUCT VERSION :
java version "1.8.0_77"
Java(TM) SE Runtime Environment (build 1.8.0_77-b03)
Java HotSpot(TM) 64-Bit Server VM (build 25.77-b03, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Windows 8.1 pro - 64 Bit (Microsoft Windows [Version 6.3.9600])

A DESCRIPTION OF THE PROBLEM :
i returned a java bean from an javascript called java function.
on this returned object i called "Object.keys" and an TypeError will be thrown

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
In the log one row will be displayed before the exception was thown:

bar



ACTUAL -
bar
object

ERROR MESSAGES/STACK TRACES THAT OCCUR :
bar
Exception in thread "main" javax.script.ScriptException: TypeError: Main$MyObject@a1153bc is not an Object in <eval> at line number 6
at jdk.nashorn.api.scripting.NashornScriptEngine.throwAsScriptException(NashornScriptEngine.java:467)
at jdk.nashorn.api.scripting.NashornScriptEngine.invokeImpl(NashornScriptEngine.java:389)
at jdk.nashorn.api.scripting.NashornScriptEngine.invokeFunction(NashornScriptEngine.java:190)
at Main.main(Main.java:92)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
Caused by: <eval>:6 TypeError: Main$MyObject@a1153bc is not an Object
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.runtime.ECMAErrors.typeError(ECMAErrors.java:172)
at jdk.nashorn.internal.objects.NativeObject.notAnObject(NativeObject.java:136)
at jdk.nashorn.internal.objects.NativeObject.keys(NativeObject.java:439)
at jdk.nashorn.internal.scripts.Script$Recompilation$1$17$\^eval\_.main(<eval>:6)
at jdk.nashorn.internal.runtime.ScriptFunctionData.invoke(ScriptFunctionData.java:640)
at jdk.nashorn.internal.runtime.ScriptFunction.invoke(ScriptFunction.java:228)
at jdk.nashorn.internal.runtime.ScriptRuntime.apply(ScriptRuntime.java:393)
at jdk.nashorn.api.scripting.ScriptObjectMirror.callMember(ScriptObjectMirror.java:199)
at jdk.nashorn.api.scripting.NashornScriptEngine.invokeImpl(NashornScriptEngine.java:383)
... 7 more

Process finished with exit code 1


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
Here is the Code:
==================== Java Start ====================
public class Main {
    public static void main(String [ ] args) throws ScriptException, NoSuchMethodException {
        ScriptEngine engine = new ScriptEngineManager().getEngineByName("nashorn");
        engine.eval(new BufferedReader(new InputStreamReader(Main.class.getResourceAsStream("/test.js"))));
        Invocable invocable = (Invocable) engine;
        invocable.invokeFunction("main");
    }

    public static MyObject getMyObject() {
        return new MyObject("bar");
    }

    public static class MyObject {
        private String foo;
        public MyObject(String foo) {
            this.foo = foo;
        }
        public String getFoo() {
            return foo;
        }
    }
}
==================== Java End =====================

============= JavaScript (test.js) Start ====================
function main () {
    var MyJavaClass = Java.type('Main');
    var test = MyJavaClass.getMyObject();
    print(test.foo);
    print(typeof Object.keys(test));
}
============= JavaScript (test.js) End ====================
---------- END SOURCE ----------