Fix signup list error when opening in new tab

src/pages/admin/signups/[id]/list.tsx

@@ -26,13 +26,19 @@ const SignupEmailPage: NextPage = () => {
   const { id } = router.query;
 
   useEffect(() => {
-    const formId = Number(id);
-    SignupApi.getForm(formId, true)
-      .then((res) => setSignupForm(res));
-
-    SignupApi.getSignups(formId).then((res) => setSignups(res));
+    const formId = id && Number(id);
+    if (formId !== undefined && !Number.isNaN(formId)) {
+      SignupApi.getForm(formId, true).then((res) => {
+        setSignupForm(res);
+      });
+      SignupApi.getSignups(formId).then((res) => {
+        setSignups(res);
+      });
+    }
   }, [id]);
 
+  const title = signupForm ? signupForm.title_fi : "Loading...";
+
   const confirmDelete = async (signup: Signup, question: any) => {
     if (window.confirm(`Delete: ${signup.id}: ${signup.answer[question.id]}; Are you sure?`) === true) {
       try {
@@ -45,27 +51,25 @@ const SignupEmailPage: NextPage = () => {
     }
   };
 
-  const title = signupForm ? signupForm.title_fi : "Loading...";
+  const renderData = () => {
+    if (!signupForm || !signups || signups.length === 0) {
+      return <div>No signups.</div>;
+    }
 
-  // TODO: ATM we filter 'info' questions from table here. Maybe remove them from answer JSON altogether?
-  const questions = signupForm ? signupForm.questions.filter((q) => q.type !== "info").map((q) => ({
-    title: q.title_fi,
-    id: q.id,
-  })) : [];
+    // TODO: ATM we filter 'info' questions from table here. Maybe remove them from answer JSON altogether?
+    const questions = signupForm ? signupForm.questions.filter((q) => q.type !== "info").map((q) => ({
+      title: q.title_fi,
+      id: q.id,
+    })) : [];
 
-  // Generate 2-dimensional array where rows are signups and columns are answers to questions.
-  const CSVData = signups.map((s) => questions.map((q) => s.answer[q.id]));
-  // Add reserve signup "header"
-  if (signupForm?.quota) {
-    CSVData.splice(signupForm.quota, 0, ["RESERVE-SIGNUPS"]);
-  }
+    // Generate 2-dimensional array where rows are signups and columns are answers to questions.
+    const CSVData = signups.map((s) => questions.map((q) => s.answer[q.id]));
+    // Add reserve signup "header"
+    if (signupForm?.quota) {
+      CSVData.splice(signupForm.quota, 0, ["RESERVE-SIGNUPS"]);
+    }
 
-  return (
-    <AdminListCommon>
-      <h1>
-        {title}
-        : Sign-ups
-      </h1>
+    return (
       <table>
         <thead>
           <tr>
@@ -81,7 +85,6 @@ const SignupEmailPage: NextPage = () => {
             </th>
           </tr>
         </thead>
-
         <tbody>
           {signups.map((s) => (
             <tr key={s.id}>
@@ -99,6 +102,16 @@ const SignupEmailPage: NextPage = () => {
           ))}
         </tbody>
       </table>
+    );
+  };
+
+  return (
+    <AdminListCommon>
+      <h1>
+        {title}
+        : Sign-ups
+      </h1>
+      {renderData()}
     </AdminListCommon>
   );
 };