code: function populatePath (options, memo, missing, fn) {
    populatePathArray.call(this, [this], options, memo, missing, (err, docs, missing) => {
      return fn(err, docs ? docs[0] : undefined, missing)
    })
  }
docs: /*!
  Populate path
  @param refs
  @param options
  @param memo
  @param missing
  @param fn