code: public static ClassNode getWrapper(ClassNode cn) {
          cn = cn.redirect();
          if (!isPrimitiveType(cn)) return cn;
  
          ClassNode result = PRIMITIVE_TYPE_TO_WRAPPER_TYPE_MAP.get(cn);
  
          if (null != result) {
              return result;
          }
  
          return cn;
      }
docs: Creates a ClassNode containing the wrapper of a ClassNode
  of primitive type. Any ClassNode representing a primitive
  type should be created using the predefined types used in
  class. The method will check the parameter for known
  references of ClassNode representing a primitive type. If
  Reference is found, then a ClassNode will be contained that
  represents the wrapper class. For example for boolean, the
  wrapper class is java.lang.Boolean.
  <p>
  If the parameter is no primitive type, the redirected
  ClassNode will be returned
  
  @param cn the ClassNode containing a possible primitive type
  @see #make(Class)
  @see #make(String)