function baseSet(object, path, value, customizer) {
      path = isKey(path, object) ? [path] : castPath(path);

      var index = -1,
          length = path.length,
          lastIndex = length - 1,
          nested = object;

      while (nested != null && ++index < length) {
        var key = toKey(path[index]);
        if (isObject(nested)) {
          var newValue = value;
          if (index != lastIndex) {
            var objValue = nested[key];
            newValue = customizer ? customizer(objValue, key, nested) : undefined;
            if (newValue === undefined) {
              newValue = objValue == null
                ? (isIndex(path[index + 1]) ? [] : {})
                : objValue;
            }
          }
          assignValue(nested, key, newValue);
        }
        nested = nested[key];
      }
      return object;
    }
The base implementation of `_.set`.

@private
@param {Object} object The object to query.
@param {Array|string} path The path of the property to set.
@param {*} value The value to set.
@param {Function} [customizer] The function to customize path creation.
@returns {Object} Returns `object`.