function joinKeyValues(object, paths, separator, filterNilValues) {
  var values = _.pickValues(object, paths);

  if(filterNilValues) {
    values = _.compact(values);
  }

  return _.join(values, separator || ',');
}
Converts all object path values into a string separated by separator.

@static
@memberOf _
@category Object
@param {Object} object The object to inspect.
@param {string|string[]} paths The property paths to pick.
@param {string} [separator=','] The element separator.
@param {Boolean} [filterNilValues=false] Ignore nil values.
@returns {string} Returns the joined string.