Fix nullable defaults for GetPropertyValueOrDefault

StabilityMatrix.Core/Extensions/JsonObjectExtensions.cs

@@ -8,10 +8,10 @@ public static class JsonObjectExtensions
     /// <summary>
     /// Returns the value of a property with the specified name, or the specified default value if not found.
     /// </summary>
-    public static T GetPropertyValueOrDefault<T>(
+    public static T? GetPropertyValueOrDefault<T>(
         this JsonObject jsonObject,
         string propertyName,
-        T defaultValue
+        T? defaultValue = default
     )
     {
         if (!jsonObject.TryGetPropertyValue(propertyName, out var node))
@@ -19,6 +19,6 @@ public static class JsonObjectExtensions
             return defaultValue;
         }
 
-        return node.Deserialize<T>() ?? defaultValue;
+        return node.Deserialize<T>();
     }
 }