code: public Object getMapValue(Object obj, String key){
          Map m = (Map) obj;
          if(!m.containsKey(key)){
              return JsonProvider.UNDEFINED;
          } else {
              return m.get(key);
          }
      }
docs: Extracts a value from an map
  
  @param obj a map
  @param key property key
  @return the map entry or {@link com.jayway.jsonpath.spi.json.JsonProvider#UNDEFINED} for missing properties