Fixing 500 error when entering a bad itemid when creating an auction

Services/AuctionService.cs

@@ -20,8 +20,13 @@ public class AuctionService
     public virtual async Task CreateAsync(Auction auction) =>
         await _auctions.InsertOneAsync(auction);
 
-    public virtual async Task<Auction> GetByIdAsync(string id) =>
-        await _auctions.Find(a => a.Id == id).FirstOrDefaultAsync();
+    public virtual async Task<Auction> GetByIdAsync(string id)
+    {
+        if (!MongoDB.Bson.ObjectId.TryParse(id, out _))
+            return null;
+
+        return await _auctions.Find(a => a.Id == id).FirstOrDefaultAsync();
+    }
 
     public virtual async Task UpdateAsync(Auction auction) =>
         await _auctions.ReplaceOneAsync(a => a.Id == auction.Id, auction);

Services/ItemService.cs

@@ -29,6 +29,9 @@ public class ItemService
 
     public virtual async Task<Item> GetByIdAsync(string id)
     {
+        if (!MongoDB.Bson.ObjectId.TryParse(id, out _))
+            return null;
+
         return await _items.Find(i => i.Id == id).FirstOrDefaultAsync();
     }