diff --git a/src/AutoMapper/Configuration/MapperConfigurationExpression.cs b/src/AutoMapper/Configuration/MapperConfigurationExpression.cs
index 6c7ad6f177..e4998d49da 100644
--- a/src/AutoMapper/Configuration/MapperConfigurationExpression.cs
+++ b/src/AutoMapper/Configuration/MapperConfigurationExpression.cs
@@ -177,7 +177,7 @@ private void AddMapsCore(IEnumerable<Assembly> assembliesToScan)
                 {
                     foreach (var memberConfigurationProvider in memberInfo.GetCustomAttributes().OfType<IMemberConfigurationProvider>())
                     {
-                        mappingExpression.ForMember(memberInfo, memberConfigurationProvider.ApplyConfiguration);
+                        mappingExpression.ForMember(memberInfo, cfg => memberConfigurationProvider.ApplyConfiguration(cfg));
                     }
                 }
 
@@ -188,5 +188,5 @@ private void AddMapsCore(IEnumerable<Assembly> assembliesToScan)
         AddProfile(autoMapAttributeProfile);
     }
 
-    public void ConstructServicesUsing(Func<Type, object> constructor) => _serviceCtor = constructor ?? throw new ArgumentNullException(nameof(constructor));
+    public void ConstructServicesUsing(Func<Type, object> constructor) => _serviceCtor = constructor;
 }
\ No newline at end of file
diff --git a/src/AutoMapper/Mapper.cs b/src/AutoMapper/Mapper.cs
index 4f82f2169d..2e3c42f997 100644
--- a/src/AutoMapper/Mapper.cs
+++ b/src/AutoMapper/Mapper.cs
@@ -1,7 +1,7 @@
 namespace AutoMapper;
+
 using IObjectMappingOperationOptions = IMappingOperationOptions<object, object>;
 using Factory = Func<Type, object>;
-#nullable enable
 public interface IMapperBase
 {
     /// <summary>
@@ -11,7 +11,7 @@ public interface IMapperBase
     /// <typeparam name="TDestination">Destination type to create</typeparam>
     /// <param name="source">Source object to map from</param>
     /// <returns>Mapped destination object</returns>
-    TDestination? Map<TDestination>(object? source);
+    TDestination Map<TDestination>(object source);
     /// <summary>
     /// Execute a mapping from the source object to a new destination object.
     /// </summary>
@@ -19,7 +19,7 @@ public interface IMapperBase
     /// <typeparam name="TDestination">Destination type to create</typeparam>
     /// <param name="source">Source object to map from</param>
     /// <returns>Mapped destination object</returns>
-    TDestination? Map<TSource, TDestination>(TSource? source);
+    TDestination Map<TSource, TDestination>(TSource source);
     /// <summary>
     /// Execute a mapping from the source object to the existing destination object.
     /// </summary>
@@ -28,7 +28,7 @@ public interface IMapperBase
     /// <param name="source">Source object to map from</param>
     /// <param name="destination">Destination object to map into</param>
     /// <returns>The mapped destination object</returns>
-    TDestination? Map<TSource, TDestination>(TSource? source, TDestination? destination);
+    TDestination Map<TSource, TDestination>(TSource source, TDestination destination);
     /// <summary>
     /// Execute a mapping from the source object to a new destination object with explicit <see cref="System.Type"/> objects
     /// </summary>
@@ -36,7 +36,7 @@ public interface IMapperBase
     /// <param name="sourceType">Source type to use</param>
     /// <param name="destinationType">Destination type to create</param>
     /// <returns>Mapped destination object</returns>
-    object? Map(object? source, Type? sourceType, Type destinationType);
+    object Map(object source, Type sourceType, Type destinationType);
     /// <summary>
     /// Execute a mapping from the source object to existing destination object with explicit <see cref="System.Type"/> objects
     /// </summary>
@@ -45,7 +45,7 @@ public interface IMapperBase
     /// <param name="sourceType">Source type to use</param>
     /// <param name="destinationType">Destination type to use</param>
     /// <returns>Mapped destination object</returns>
-    object? Map(object? source, object? destination, Type? sourceType, Type? destinationType);
+    object Map(object source, object destination, Type sourceType, Type destinationType);
 }
 public interface IMapper : IMapperBase
 {
@@ -56,7 +56,7 @@ public interface IMapper : IMapperBase
     /// <param name="source">Source object to map from</param>
     /// <param name="opts">Mapping options</param>
     /// <returns>Mapped destination object</returns>
-    TDestination? Map<TDestination>(object? source, Action<IMappingOperationOptions<object, TDestination>> opts);
+    TDestination Map<TDestination>(object source, Action<IMappingOperationOptions<object, TDestination>> opts);
     /// <summary>
     /// Execute a mapping from the source object to a new destination object with supplied mapping options.
     /// </summary>
@@ -65,7 +65,7 @@ public interface IMapper : IMapperBase
     /// <param name="source">Source object to map from</param>
     /// <param name="opts">Mapping options</param>
     /// <returns>Mapped destination object</returns>
-    TDestination? Map<TSource, TDestination>(TSource? source, Action<IMappingOperationOptions<TSource, TDestination>> opts);
+    TDestination Map<TSource, TDestination>(TSource source, Action<IMappingOperationOptions<TSource, TDestination>> opts);
     /// <summary>
     /// Execute a mapping from the source object to the existing destination object with supplied mapping options.
     /// </summary>
@@ -75,7 +75,7 @@ public interface IMapper : IMapperBase
     /// <param name="destination">Destination object to map into</param>
     /// <param name="opts">Mapping options</param>
     /// <returns>The mapped destination object</returns>
-    TDestination? Map<TSource, TDestination>(TSource? source, TDestination? destination, Action<IMappingOperationOptions<TSource, TDestination>> opts);
+    TDestination Map<TSource, TDestination>(TSource source, TDestination destination, Action<IMappingOperationOptions<TSource, TDestination>> opts);
     /// <summary>
     /// Execute a mapping from the source object to a new destination object with explicit <see cref="System.Type"/> objects and supplied mapping options.
     /// </summary>
@@ -84,7 +84,7 @@ public interface IMapper : IMapperBase
     /// <param name="destinationType">Destination type to create</param>
     /// <param name="opts">Mapping options</param>
     /// <returns>Mapped destination object</returns>
-    object? Map(object? source, Type? sourceType, Type destinationType, Action<IObjectMappingOperationOptions> opts);
+    object Map(object source, Type sourceType, Type destinationType, Action<IObjectMappingOperationOptions> opts);
     /// <summary>
     /// Execute a mapping from the source object to existing destination object with supplied mapping options and explicit <see cref="System.Type"/> objects
     /// </summary>
@@ -94,7 +94,7 @@ public interface IMapper : IMapperBase
     /// <param name="destinationType">Destination type to use</param>
     /// <param name="opts">Mapping options</param>
     /// <returns>Mapped destination object</returns>
-    object? Map(object? source, object? destination, Type? sourceType, Type? destinationType, Action<IObjectMappingOperationOptions> opts);
+    object Map(object source, object destination, Type sourceType, Type destinationType, Action<IObjectMappingOperationOptions> opts);
     /// <summary>
     /// Configuration provider for performing maps
     /// </summary>
@@ -108,7 +108,7 @@ public interface IMapper : IMapperBase
     /// <param name="parameters">Optional parameter object for parameterized mapping expressions</param>
     /// <param name="membersToExpand">Explicit members to expand</param>
     /// <returns>Queryable result, use queryable extension methods to project and execute result</returns>
-    IQueryable<TDestination> ProjectTo<TDestination>(IQueryable source, object? parameters = null, params Expression<Func<TDestination, object>>[] membersToExpand);
+    IQueryable<TDestination> ProjectTo<TDestination>(IQueryable source, object parameters = null, params Expression<Func<TDestination, object>>[] membersToExpand);
     /// <summary>
     /// Project the input queryable.
     /// </summary>
@@ -117,7 +117,7 @@ public interface IMapper : IMapperBase
     /// <param name="parameters">Optional parameter object for parameterized mapping expressions</param>
     /// <param name="membersToExpand">Explicit members to expand</param>
     /// <returns>Queryable result, use queryable extension methods to project and execute result</returns>
-    IQueryable<TDestination> ProjectTo<TDestination>(IQueryable source, IDictionary<string, object>? parameters, params string[] membersToExpand);
+    IQueryable<TDestination> ProjectTo<TDestination>(IQueryable source, IDictionary<string, object> parameters, params string[] membersToExpand);
     /// <summary>
     /// Project the input queryable.
     /// </summary>
@@ -126,12 +126,11 @@ public interface IMapper : IMapperBase
     /// <param name="parameters">Optional parameter object for parameterized mapping expressions</param>
     /// <param name="membersToExpand">Explicit members to expand</param>
     /// <returns>Queryable result, use queryable extension methods to project and execute result</returns>
-    IQueryable ProjectTo(IQueryable source, Type destinationType, IDictionary<string, object>? parameters = null, params string[] membersToExpand);
+    IQueryable ProjectTo(IQueryable source, Type destinationType, IDictionary<string, object> parameters = null, params string[] membersToExpand);
 }
 public interface IRuntimeMapper : IMapperBase
 {
 }
-#nullable disable
 internal interface IInternalRuntimeMapper : IRuntimeMapper
 {
     TDestination Map<TSource, TDestination>(TSource source, TDestination destination, ResolutionContext context, Type sourceType = null, Type destinationType = null, MemberMap memberMap = null);
diff --git a/src/AutoMapper/QueryableExtensions/Extensions.cs b/src/AutoMapper/QueryableExtensions/Extensions.cs
index 5bad8cd9fc..6ecb99e1fa 100644
--- a/src/AutoMapper/QueryableExtensions/Extensions.cs
+++ b/src/AutoMapper/QueryableExtensions/Extensions.cs
@@ -1,4 +1,5 @@
 namespace AutoMapper.QueryableExtensions;
+
 using MemberPaths = IEnumerable<MemberInfo[]>;
 using ParameterBag = IDictionary<string, object>;
 /// <summary>
@@ -19,8 +20,7 @@ public static class Extensions
     /// <param name="parameters">Optional parameter object for parameterized mapping expressions</param>
     /// <param name="membersToExpand">Explicit members to expand</param>
     /// <returns>Expression to project into</returns>
-#nullable enable
-    public static IQueryable<TDestination> ProjectTo<TDestination>(this IQueryable source, IConfigurationProvider configuration, object? parameters, params Expression<Func<TDestination, object>>[] membersToExpand) =>
+    public static IQueryable<TDestination> ProjectTo<TDestination>(this IQueryable source, IConfigurationProvider configuration, object parameters, params Expression<Func<TDestination, object>>[] membersToExpand) =>
         source.ToCore<TDestination>(configuration, parameters, membersToExpand.Select(MemberVisitor.GetMemberPath));
     /// <summary>
     /// Extension method to project from a queryable using the provided mapping engine
@@ -43,7 +43,7 @@ public static class Extensions
     /// <param name="parameters">Optional parameter object for parameterized mapping expressions</param>
     /// <param name="membersToExpand">Explicit members to expand</param>
     /// <returns>Queryable result, use queryable extension methods to project and execute result</returns>
-    public static IQueryable<TDestination> ProjectTo<TDestination>(this IQueryable source, IConfigurationProvider configuration, ParameterBag? parameters, params string[] membersToExpand) =>
+    public static IQueryable<TDestination> ProjectTo<TDestination>(this IQueryable source, IConfigurationProvider configuration, ParameterBag parameters, params string[] membersToExpand) =>
         source.ToCore<TDestination>(configuration, parameters, membersToExpand.Select(memberName => ReflectionHelper.GetMemberPath(typeof(TDestination), memberName)));
     /// <summary>
     /// Extension method to project from a queryable using the provided mapping engine
@@ -64,9 +64,8 @@ public static class Extensions
     /// <param name="parameters">Optional parameter object for parameterized mapping expressions</param>
     /// <param name="membersToExpand">Explicit members to expand</param>
     /// <returns>Queryable result, use queryable extension methods to project and execute result</returns>
-    public static IQueryable ProjectTo(this IQueryable source, Type destinationType, IConfigurationProvider configuration, ParameterBag? parameters, params string[] membersToExpand) =>
+    public static IQueryable ProjectTo(this IQueryable source, Type destinationType, IConfigurationProvider configuration, ParameterBag parameters, params string[] membersToExpand) =>
         source.ToCore(destinationType, configuration, parameters, membersToExpand.Select(memberName => ReflectionHelper.GetMemberPath(destinationType, memberName)));
-#nullable disable
     static IQueryable<TResult> ToCore<TResult>(this IQueryable source, IConfigurationProvider configuration, object parameters, MemberPaths memberPathsToExpand) =>
         (IQueryable<TResult>)source.ToCore(typeof(TResult), configuration, parameters, memberPathsToExpand);
     static IQueryable ToCore(this IQueryable source, Type destinationType, IConfigurationProvider configuration, object parameters, MemberPaths memberPathsToExpand) =>