code: public Map<String, Object> getContext() {
          final Map<String, Object> rval = newMap();
          rval.putAll(context);
          // replace "" with "@vocab"
          if (rval.containsKey("")) {
              rval.put("@vocab", rval.remove(""));
          }
          return rval;
      }
docs: Returns a valid context containing any namespaces set
  
  @return The context map