code: public SqlVisitor create(String tagName) {
          Class<?> aClass = tagToClassMap.get(tagName);
          if (aClass == null) {
              return null;
          }
          try {
              return (SqlVisitor) aClass.getConstructor().newInstance();
          } catch (Exception e) {
              throw new RuntimeException(e);
          }
      }
docs: Create a new Change subclass based on the given tag name.