public OgnlStack(Object obj){
this(obj,new HashMap<String, Object>());
}
public OgnlStack(Object obj, Map<String,Object> context){
NullHandler nullHandler = null;
synchronized (OgnlStack.class) {
try {
nullHandler = OgnlRuntime.getNullHandler(Object.class);
if(nullHandler == null || !(nullHandler instanceof InstantiatingNullHandler))
OgnlRuntime.setNullHandler(Object.class, new InstantiatingNullHandler(nullHandler, Arrays.asList("java")));