ensure fallback certificates of all domains

https://forum.cloudron.io/topic/5683/data-argument-must-be-of-type-received-null-error-during-restore-process

src/test/reverseproxy-test.js

@@ -131,7 +131,6 @@ describe('Reverse Proxy', function () {
         it('can generate fallback certs', async function () {
             result = await reverseProxy.generateFallbackCertificate(domainObject.domain);
             expect(result).to.be.ok();
-            expect(result.error).to.be(null);
         });
 
         it('can validate the certs', function () {