The value created_on can be null

src/CloudFlare.NET/DnsRecord.cs

@@ -24,7 +24,7 @@ public DnsRecord(
             int ttl,
             bool locked,
             IdentifierTag zoneId,
-            DateTimeOffset createdOn,
+            DateTimeOffset? createdOn,
             DateTimeOffset modifiedOn,
             int priority,
             string content = null,
@@ -120,7 +120,7 @@ public DnsRecord(
         /// When the record was created.
         /// </summary>
         [JsonProperty("created_on")]
-        public DateTimeOffset CreatedOn { get; }
+        public DateTimeOffset? CreatedOn { get; }
 
         /// <summary>
         /// When the record was last modified.

src/CloudFlare.NET/Zone.cs

@@ -20,7 +20,7 @@ public Zone(
             IdentifierTag id,
             string name,
             int developmentMode,
-            DateTimeOffset createdOn,
+            DateTimeOffset? createdOn,
             DateTimeOffset modifiedOn,
             IReadOnlyList<string> originalNameServers = null,
             string originalRegistrar = null,
@@ -84,7 +84,7 @@ public Zone(
         /// When the zone was created.
         /// </summary>
         [JsonProperty("created_on")]
-        public DateTimeOffset CreatedOn { get; }
+        public DateTimeOffset? CreatedOn { get; }
 
         /// <summary>
         /// When the zone was last modified.

src/Tests/CloudFlare.NET.Tests/CloudFlare.NET.Tests.csproj

@@ -106,6 +106,7 @@
     <Compile Include="EqualsBehaviors.cs" />
     <Compile Include="FixtureContext.cs" />
     <Compile Include="IdentifierTagSpec.cs" />
+    <Compile Include="IsNullable.cs" />
     <Compile Include="LikenessExtensions.cs" />
     <Compile Include="RequiresArgNullEx.cs" />
     <Compile Include="RequiresArgNullExAutoMoqAttribute.cs" />

src/Tests/CloudFlare.NET.Tests/IsNullable.cs

@@ -0,0 +1,37 @@
+namespace CloudFlare.NET
+{
+    using System;
+    using System.Collections.Generic;
+    using System.Linq;
+    using System.Reflection;
+    using AutoTest.ArgNullEx.Filter;
+
+    /// <summary>
+    /// Filters out parameters that are <see cref="Nullable"/> value types.
+    /// </summary>
+    public sealed class IsNullable : FilterBase, IParameterFilter
+    {
+        /// <summary>
+        /// Filters out parameters that are <see cref="Nullable"/> value types.
+        /// </summary>
+        /// <param name="type">The type.</param>
+        /// <param name="method">The method.</param>
+        /// <param name="parameter">The parameter.</param>
+        /// <returns><see langword="true"/> if the <paramref name="parameter"/> should be excluded;
+        /// otherwise <see langword="false"/>.</returns>
+        /// <exception cref="ArgumentNullException">The <paramref name="type"/>, <paramref name="method"/> or
+        /// <paramref name="parameter"/> parameters are <see langword="null"/>.</exception>
+        bool IParameterFilter.ExcludeParameter(Type type, MethodBase method, ParameterInfo parameter)
+        {
+            if (type == null)
+                throw new ArgumentNullException(nameof(type));
+            if (method == null)
+                throw new ArgumentNullException(nameof(method));
+            if (parameter == null)
+                throw new ArgumentNullException(nameof(parameter));
+
+            return parameter.ParameterType.IsGenericType &&
+                   parameter.ParameterType.GetGenericTypeDefinition() == typeof(Nullable<>);
+        }
+    }
+}

src/Tests/CloudFlare.NET.Tests/Serialization/DnsRecordMinimal.json

@@ -1,5 +1,6 @@
 {
     "id": "9a7806061c88ada191ed06f989cc3dac",
     "name": "example.com",
-    "zone_id": "9a7806061c88ada191ed06f989cc3dac"
+    "zone_id": "9a7806061c88ada191ed06f989cc3dac",
+    "created_on": null
 }

src/Tests/CloudFlare.NET.Tests/Serialization/ZoneMinimal.json

@@ -1,4 +1,5 @@
 {
     "id": "9a7806061c88ada191ed06f989cc3dac",
-    "name": "example.com"
+    "name": "example.com",
+    "created_on": null
 }