code: function assignMergeValue(object, key, value) {
        if ((value !== undefined$1 && !eq(object[key], value)) ||
            (value === undefined$1 && !(key in object))) {
          baseAssignValue(object, key, value);
        }
      }
docs: This function is like `assignValue` except that it doesn't assign
  `undefined` values.
  
  @private
  @param {Object} object The object to modify.
  @param {string} key The key of the property to assign.
  @param {*} value The value to assign.