fix: registration without email

src/routes/Register.svelte

@@ -32,10 +32,16 @@
 
 	async function register() {
 		try {
+			let emailToSend = null;
+			if (email !== '') {
+				if (email.includes('@')) {
+					emailToSend = email;
+				}
+			}
 			response = (await RunnerService.runnerControllerPost({
 				firstname,
 				lastname,
-				email,
+				email: emailToSend,
 				group
 			})) as ResponseRunner;
 			showResult = true;