t0302: check helper can handle empty credentials

Make sure the helper does not crash when blank username and password is
provided. If the helper can save such credentials, it should be able to
read them back.

Signed-off-by: Jakub Bereżański <kuba@berezanscy.pl>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/lib-credential.sh

@@ -44,6 +44,7 @@ helper_test_clean() {
 	reject $1 https example.com user2
 	reject $1 http path.tld user
 	reject $1 https timeout.tld user
+	reject $1 https sso.tld
 }
 
 reject() {
@@ -250,6 +251,24 @@ helper_test() {
 		password=pass2
 		EOF
 	'
+
+	test_expect_success "helper ($HELPER) can store empty username" '
+		check approve $HELPER <<-\EOF &&
+		protocol=https
+		host=sso.tld
+		username=
+		password=
+		EOF
+		check fill $HELPER <<-\EOF
+		protocol=https
+		host=sso.tld
+		--
+		protocol=https
+		host=sso.tld
+		username=
+		password=
+		EOF
+	'
 }
 
 helper_test_timeout() {