Bug fixes:

Assign idempotency test result to the correct var
Handle case when username/password is not specified

api/api.go

diff --git a/api/api.go b/api/api.go
index 9542368..71e9b43 100644
--- a/api/api.go
+++ b/api/api.go
@@ -80,11 +80,14 @@
 // with a given server address and username/password.
 func InitHTTPConnection(serverAddr string, credentialsFile string, caFile string, fullServerName string) (*HTTPConnection, error) {
 	// Set up username/password.
-	data, err := ioutil.ReadFile(credentialsFile)
-	if err != nil {
-		return nil, err
+	var credentials string
+	if credentialsFile != "" {
+		data, err := ioutil.ReadFile(credentialsFile)
+		if err != nil {
+			return nil, err
+		}
+		credentials = "Basic " + base64.StdEncoding.EncodeToString([]byte(strings.Replace(string(data), "\n", "", -1)))
 	}
-	usernamePassword := strings.Replace(string(data), "\n", "", -1)
 	config, err := setupCertConfig(caFile, fullServerName)
 	if err != nil {
 		return nil, err
@@ -98,7 +101,7 @@
 			Timeout:   10 * time.Second,
 			Transport: &http.Transport{TLSClientConfig: config},
 		},
-		credentials: "Basic " + base64.StdEncoding.EncodeToString([]byte(usernamePassword)),
+		credentials: credentials,
 		marshaler:   &jsonpb.Marshaler{OrigName: true},
 		baseURL:     protocol + "://" + serverAddr,
 	}, nil