🐛 fix(TypeAdapter.cs): make source parameter nullable

The source parameter in the Adapt method is now nullable, which allows for null values to be passed in without throwing a null reference exception. This improves the robustness of the code and makes it more defensive against unexpected null values.

src/Mapster/TypeAdapter.cs

@@ -21,7 +21,7 @@ public static TypeAdapterBuilder<TSource> BuildAdapter<TSource>(this TSource sou
  /// <typeparam name="TDestination">Destination type.</typeparam>
  /// <param name="source">Source object to adapt.</param>
  /// <returns>Adapted destination type.</returns>
- public static TDestination Adapt<TDestination>(this object source)
+ public static TDestination Adapt<TDestination>(this object? source)
  {
  return Adapt<TDestination>(source, TypeAdapterConfig.GlobalSettings);
  }
@@ -33,7 +33,7 @@ public static TDestination Adapt<TDestination>(this object source)
  /// <param name="source">Source object to adapt.</param>
  /// <param name="config">Configuration</param>
  /// <returns>Adapted destination type.</returns>
- public static TDestination Adapt<TDestination>(this object source, TypeAdapterConfig config)
+ public static TDestination Adapt<TDestination>(this object? source, TypeAdapterConfig config)
  {
  // ReSharper disable once ConditionIsAlwaysTrueOrFalse
  if (source == null)