fix: use normalized domains in getMainCustomDomain()

getMainCustomDomain() was reading the raw configuration.domain,
so an empty string "" would be returned as-is, producing a URL
like "https://" instead of falling back to the CloudFront domain.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: mnapoli

src/constructs/aws/ServerSideWebsite.ts

@@ -349,12 +349,12 @@ export class ServerSideWebsite extends AwsConstruct {
     }
 
     getMainCustomDomain(): string | undefined {
-        if (this.configuration.domain === undefined) {
+        if (this.domains === undefined || this.domains.length === 0) {
             return undefined;
         }
 
         // In case of multiple domains, we take the first one
-        return typeof this.configuration.domain === "string" ? this.configuration.domain : this.configuration.domain[0];
+        return this.domains[0];
     }
 
     private createCacheBehaviors(bucket: Bucket): Record<string, BehaviorOptions> {

test/unit/serverSideWebsite.test.ts

@@ -631,6 +631,13 @@ describe("server-side website", () => {
         expect(cfTemplate.Resources[cfDistributionLogicalId]).not.toHaveProperty(
             "Properties.DistributionConfig.ViewerCertificate"
         );
+        // The domain output should fall back to the CloudFront domain
+        expect(cfTemplate.Outputs).toMatchObject({
+            [computeLogicalId("backend", "Domain")]: {
+                Description: "Website domain name.",
+                Value: { "Fn::GetAtt": [cfDistributionLogicalId, "DomainName"] },
+            },
+        });
     });
 
     it("should treat empty string domain with valid certificate as unconfigured", async () => {