Overhaul ValuesJsonConverter

Source/Schema.NET/OneOrMany{T}.cs

@@ -69,6 +69,38 @@ public OneOrMany(List<T> list)
             }
         }
 
+        /// <summary>
+        /// Initializes a new instance of the <see cref="OneOrMany{T}"/> struct.
+        /// </summary>
+        /// <param name="list">The list of values.</param>
+        public OneOrMany(IEnumerable<object> list)
+        {
+            if (list is null)
+            {
+                throw new ArgumentNullException(nameof(list));
+            }
+
+            var items = new List<T>();
+            foreach (var item in list)
+            {
+                if (item is T itemT)
+                {
+                    items.Add(itemT);
+                }
+            }
+
+            if (items.Count == 1)
+            {
+                this.collection = null;
+                this.item = items[0];
+            }
+            else
+            {
+                this.collection = items;
+                this.item = default;
+            }
+        }
+
         /// <summary>
         /// Gets the number of elements contained in the <see cref="OneOrMany{T}"/>.
         /// </summary>

Source/Schema.NET/TimeSpanToISO8601DurationValuesJsonConverter.cs

@@ -12,46 +12,6 @@ namespace Schema.NET
     /// <seealso cref="ValuesJsonConverter" />
     public class TimeSpanToISO8601DurationValuesJsonConverter : ValuesJsonConverter
     {
-        /// <inheritdoc />
-        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
-        {
-            if (reader is null)
-            {
-                throw new ArgumentNullException(nameof(reader));
-            }
-
-            if (objectType is null)
-            {
-                throw new ArgumentNullException(nameof(objectType));
-            }
-
-            if (serializer is null)
-            {
-                throw new ArgumentNullException(nameof(serializer));
-            }
-
-            var valuesType = objectType.GetUnderlyingTypeFromNullable();
-            if (valuesType != null && valuesType.GenericTypeArguments.Length == 1)
-            {
-                var mainType = valuesType.GenericTypeArguments[0];
-                var genericType = typeof(OneOrMany<TimeSpan>);
-                if (mainType.IsNullable())
-                {
-                    mainType = Nullable.GetUnderlyingType(mainType);
-                    genericType = typeof(OneOrMany<TimeSpan?>);
-                }
-
-                if (mainType == typeof(TimeSpan))
-                {
-                    var timeSpan = XmlConvert.ToTimeSpan(reader.Value.ToString());
-                    var instance = Activator.CreateInstance(genericType, timeSpan);
-                    return instance;
-                }
-            }
-
-            return base.ReadJson(reader, objectType, existingValue, serializer);
-        }
-
         /// <summary>
         /// Writes the object retrieved from <see cref="IValues"/> when one is found.
         /// </summary>