Return default value when getting 'null' for a setting in `PSConfigur…

…ation.cs` (#10963)

src/System.Management.Automation/engine/PSConfiguration.cs

@@ -439,7 +439,7 @@ private T ReadValueFromFile<T>(ConfigScope scope, string key, T defaultValue = d
 
             if (configData != emptyConfig && configData.TryGetValue(key, StringComparison.OrdinalIgnoreCase, out JToken jToken))
             {
-                return jToken.ToObject<T>(serializer);
+                return jToken.ToObject<T>(serializer) ?? defaultValue;
             }
 
             return defaultValue;