Fix firefox forwarder when website isn't set (#487)

## Type of change
```
- [x] Bug fix
- [ ] New feature development
- [ ] Tech debt (refactoring, code cleanup, dependency upgrades, etc)
- [ ] Build/deploy pipeline (DevOps)
- [ ] Other
```

## Objective
When the website parameter is None, the request would include a
`generated_for: null` field, while the API expects the field to not be
present.

crates/bitwarden/src/tool/generators/username_forwarders/firefox.rs

@@ -22,6 +22,7 @@ async fn generate_with_api_url(
     #[derive(serde::Serialize)]
     struct Request {
         enabled: bool,
+        #[serde(skip_serializing_if = "Option::is_none")]
         generated_for: Option<String>,
         description: String,
     }
@@ -58,13 +59,13 @@ async fn generate_with_api_url(
 #[cfg(test)]
 mod tests {
     use serde_json::json;
+
     #[tokio::test]
-    async fn test_mock_server() {
+    async fn test_mock_success() {
         use wiremock::{matchers, Mock, ResponseTemplate};
 
-        let (server, _client) = crate::util::start_mock(vec![
-            // Mock the request to the Firefox API, and verify that the correct request is made
-            Mock::given(matchers::path("/api/v1/relayaddresses/"))
+        let (server, _client) =
+            crate::util::start_mock(vec![Mock::given(matchers::path("/api/v1/relayaddresses/"))
                 .and(matchers::method("POST"))
                 .and(matchers::header("Content-Type", "application/json"))
                 .and(matchers::header("Authorization", "Token MY_TOKEN"))
@@ -76,33 +77,73 @@ mod tests {
                 .respond_with(ResponseTemplate::new(201).set_body_json(json!({
                     "full_address": "ofuj4d4qw@mozmail.com"
                 })))
-                .expect(1),
-            // Mock an invalid API key
-            Mock::given(matchers::path("/api/v1/relayaddresses/"))
+                .expect(1)])
+            .await;
+
+        let address = super::generate_with_api_url(
+            &reqwest::Client::new(),
+            "MY_TOKEN".into(),
+            Some("example.com".into()),
+            format!("http://{}", server.address()),
+        )
+        .await
+        .unwrap();
+        assert_eq!(address, "ofuj4d4qw@mozmail.com");
+
+        server.verify().await;
+    }
+
+    #[tokio::test]
+    async fn test_mock_without_website() {
+        use wiremock::{matchers, Mock, ResponseTemplate};
+
+        let (server, _client) =
+            crate::util::start_mock(vec![Mock::given(matchers::path("/api/v1/relayaddresses/"))
                 .and(matchers::method("POST"))
                 .and(matchers::header("Content-Type", "application/json"))
-                .and(matchers::header("Authorization", "Token MY_FAKE_TOKEN"))
+                .and(matchers::header("Authorization", "Token MY_OTHER_TOKEN"))
                 .and(matchers::body_json(json!({
                     "enabled": true,
-                    "generated_for": "example.com",
-                    "description": "example.com - Generated by Bitwarden."
+                    "description": "Generated by Bitwarden."
                 })))
-                .respond_with(ResponseTemplate::new(401))
-                .expect(1),
-        ])
-        .await;
+                .respond_with(ResponseTemplate::new(201).set_body_json(json!({
+                    "full_address": "856f7765@mozmail.com"
+                })))
+                .expect(1)])
+            .await;
 
         let address = super::generate_with_api_url(
             &reqwest::Client::new(),
-            "MY_TOKEN".into(),
-            Some("example.com".into()),
+            "MY_OTHER_TOKEN".into(),
+            None,
             format!("http://{}", server.address()),
         )
         .await
         .unwrap();
-        assert_eq!(address, "ofuj4d4qw@mozmail.com");
+        assert_eq!(address, "856f7765@mozmail.com");
+
+        server.verify().await;
+    }
+
+    #[tokio::test]
+    async fn test_mock_invalid_token() {
+        use wiremock::{matchers, Mock, ResponseTemplate};
+
+        let (server, _client) =
+            crate::util::start_mock(vec![Mock::given(matchers::path("/api/v1/relayaddresses/"))
+                .and(matchers::method("POST"))
+                .and(matchers::header("Content-Type", "application/json"))
+                .and(matchers::header("Authorization", "Token MY_FAKE_TOKEN"))
+                .and(matchers::body_json(json!({
+                    "enabled": true,
+                    "generated_for": "example.com",
+                    "description": "example.com - Generated by Bitwarden."
+                })))
+                .respond_with(ResponseTemplate::new(401))
+                .expect(1)])
+            .await;
 
-        let fake_token_error = super::generate_with_api_url(
+        let error = super::generate_with_api_url(
             &reqwest::Client::new(),
             "MY_FAKE_TOKEN".into(),
             Some("example.com".into()),
@@ -111,9 +152,7 @@ mod tests {
         .await
         .unwrap_err();
 
-        assert!(fake_token_error
-            .to_string()
-            .contains("Invalid Firefox Relay API key"));
+        assert!(error.to_string().contains("Invalid Firefox Relay API key"));
 
         server.verify().await;
     }