client: specify default behavior upon nil Roundtripper
@@ -57,6 +57,8 @@ type NotaryRepository struct {
// a file cache from the provided repository, local config information and a crypto service.
// It also retrieves the remote store associated to the base directory under where all the
// trust files will be stored and the specified GUN.
+//
+// In case of a nil RoundTripper, a default offline store is used instead.
func NewFileCachedNotaryRepository(baseDir string, gun data.GUN, baseURL string, rt http.RoundTripper,
retriever notary.PassRetriever, trustPinning trustpinning.TrustPinConfig) (
*NotaryRepository, error) {
