whole_func_string: function _normalizeError(onError) {
              var _onError = onError;
              if (onError.length < 2 || 3 < onError.length) {
                  throw new Error(onError.name + ': args length invalid. should be: onError(err, next)');
              }
              return _onError;
          }
func_code_string: function _normalizeError(onError) {
              var _onError = onError;
              if (onError.length < 2 || 3 < onError.length) {
                  throw new Error(onError.name + ': args length invalid. should be: onError(err, next)');
              }
              return _onError;
          }
func_documentation_string: errorのコールバックをラップして引数を共通化します
  @memberof Bucks
  @instance
  @private
  @param {Function} onError ex) onError(err, next)
  @throws {Error} args length invalid
  @return {function} wrappedTask ex) onError(err, next)