fix: fix bug in MapsterMapper#903. Drop collect ctor param with Getter == null

Author: DocSvartz

src/Mapster/Adapters/BaseClassAdapter.cs

@@ -220,7 +220,7 @@ protected Expression CreateInstantiationExpression(Expression source, ClassMappi
             var arguments = new List<Expression>();
             foreach (var member in members)
             {
-                arg.Context.NullChecks.UnionWith(members.Select(x=>(x.Getter,arg)));
+                arg.Context.NullChecks.UnionWith(members.Where(x=>x.Getter != null).Select(x=>(x.Getter,arg)));
                 var parameterInfo = (ParameterInfo)member.DestinationMember.Info!;
                 var defaultConst = parameterInfo.IsOptional
                     ? Expression.Constant(parameterInfo.DefaultValue, member.DestinationMember.Type)

src/Mapster/Utils/ExpressionEx.cs

@@ -436,11 +436,14 @@ public static Expression ApplyNullPropagation(this Expression getter)
 
         public static Expression ApplyNullPropagationFromCtor(this Expression getter, Expression adapt, CompileArgument arg)
         {
+            if (getter == null)
+                return adapt;
+
             Expression? condition = null;
             var current = getter;
             var checks = arg.Context.NullChecks
                 .Where(x=> !object.ReferenceEquals(x.arg,arg))
-                .Select(x=>x.param.Type);
+                .Select(x=>x.param?.Type);
 
             while (current != null) 
             {