Fix Firestore undefined value error when creating prayers

src/app/page.tsx

@@ -102,15 +102,21 @@ export default function Home() {
     }
 
     try {
-      const prayerData = {
+      const prayerData: any = {
         userId: user.uid,
         date,
         text,
-        prayFor: prayFor || undefined,
         answered,
-        answerDetails: answerDetails || undefined,
       };
 
+      // Only add optional fields if they have values
+      if (prayFor) {
+        prayerData.prayFor = prayFor;
+      }
+      if (answerDetails) {
+        prayerData.answerDetails = answerDetails;
+      }
+
       if (editingPrayer) {
         // Update existing prayer
         await updateDoc(doc(db, 'prayers', editingPrayer.id), prayerData);