Let's try https://stackoverflow.com/questions/58443181/does-the-new-system-text-json-have-a-required-property-attribute

Author: Trolldemorted

EnoCore/Models/CheckerTaskMessage.cs

@@ -1,16 +1,72 @@
 namespace EnoCore.Models
 {
-    public sealed record CheckerTaskMessage(
-        long TaskId,
-        CheckerTaskMethod Method,
-        string Address,
-        long TeamId,
-        string TeamName,
-        long CurrentRoundId,
-        long RelatedRoundId,
-        string? Flag,
-        long VariantId,
-        long Timeout,
-        long RoundLength,
-        string TaskChainId);
+    using System;
+    using System.Diagnostics.CodeAnalysis;
+
+    public class CheckerTaskMessage
+    {
+        public CheckerTaskMessage(
+            long? taskId,
+            CheckerTaskMethod? method,
+            string? address,
+            long? teamId,
+            string? teamName,
+            long? currentRoundId,
+            long? relatedRoundId,
+            string? flag,
+            long? variantId,
+            long? timeout,
+            long? roundLength,
+            string? taskChainId)
+        {
+            this.TaskId = taskId ?? throw new ArgumentNullException(nameof(taskId));
+            this.Method = method ?? throw new ArgumentNullException(nameof(method));
+            this.Address = address ?? throw new ArgumentNullException(nameof(address));
+            this.TeamId = teamId ?? throw new ArgumentNullException(nameof(teamId));
+            this.TeamName = teamName ?? throw new ArgumentNullException(nameof(teamName));
+            this.CurrentRoundId = currentRoundId ?? throw new ArgumentNullException(nameof(currentRoundId));
+            this.RelatedRoundId = relatedRoundId ?? throw new ArgumentNullException(nameof(relatedRoundId));
+            this.Flag = flag ?? throw new ArgumentNullException(nameof(flag));
+            this.VariantId = variantId ?? throw new ArgumentNullException(nameof(variantId));
+            this.Timeout = timeout ?? throw new ArgumentNullException(nameof(timeout));
+            this.RoundLength = roundLength ?? throw new ArgumentNullException(nameof(roundLength));
+            this.TaskChainId = taskChainId ?? throw new ArgumentNullException(nameof(taskChainId));
+        }
+
+        [NotNull]
+        public long? TaskId { get; }
+
+        [NotNull]
+        public CheckerTaskMethod? Method { get; }
+
+        [NotNull]
+        public string? Address { get; }
+
+        [NotNull]
+        public long? TeamId { get; }
+
+        [NotNull]
+        public string? TeamName { get; }
+
+        [NotNull]
+        public long? CurrentRoundId { get; }
+
+        [NotNull]
+        public long? RelatedRoundId { get; }
+
+        [NotNull]
+        public string? Flag { get; }
+
+        [NotNull]
+        public long? VariantId { get; }
+
+        [NotNull]
+        public long? Timeout { get; }
+
+        [NotNull]
+        public long? RoundLength { get; }
+
+        [NotNull]
+        public string? TaskChainId { get; }
+    }
 }