function makeSingles(arr) {
    const ret = [];
    arr.forEach(function(obj) {
      if (oneSpaceRE.test(obj.path)) {
        const paths = obj.path.split(manySpaceRE);
        paths.forEach(function(p) {
          const copy = Object.assign({}, obj);
          copy.path = p;
          ret.push(copy);
        });
      } else {
        ret.push(obj);
      }
    });

    return ret;
  }
populate helper
@param {String} path
@param {String} select
@param {Model} model
@param {Object} match
@param {Object} options
@param {Any} subPopulate
@param {Boolean} justOne
@param {Boolean} count