docs: function validateSaveLoadParameters(that, method, file, cb, options) {
          if ('string' !== typeof file || file.trim() === '') {
              that.throwErr('TypeError', method, 'file must be ' +
                            'a non-empty string');
          }
          if (cb && 'function' !== typeof cb) {
              that.throwErr('TypeError', method, 'cb must be function ' +
                            'or undefined');
          }
          if (options && 'object' !== typeof options) {
              that.throwErr('TypeError', method, 'options must be object ' +
                            'or undefined');
          }
      }