Consider the following methods:
http://docs.oracle.com/javase/8/docs/api/javax/script/ScriptContext.html#getAttribute-java.lang.String-int-
http://docs.oracle.com/javase/8/docs/api/javax/script/ScriptContext.html#removeAttribute-java.lang.String-int-

For attribute names which are undefined they behave differently for Nashorn:

        new ScriptEngineManager()
            .getEngineFactories()
            .stream()
            .map(ScriptEngineFactory::getScriptEngine)
            .map((engine) -> {
                System.err.println("engine = " + engine);
                return engine.getContext();
            })
            .forEach(c -> {
                System.err.println("context = " + c);
                System.err.println("get returns = " + c.getAttribute("undefinedname", ScriptContext.ENGINE_SCOPE));
                System.err.println("remove returns = " + c.removeAttribute("undefinedname", ScriptContext.ENGINE_SCOPE));
            });


When run v.s. OracleJDK the output will be like:


engine = jdk.nashorn.api.scripting.NashornScriptEngine@f3eef9
context = javax.script.SimpleScriptContext@3c4f91
get returns = null
remove returns = undefined


The following JCK9 test fails due to this:

api/javax_script/ScriptContext/index.html#SetGetAttribute[remove_noValueDefined]