At first glance, this looks like a bug. I will attempt to reproduce this with a regression test and see if I can pinpoint the problem. Is it possible for you to post a stack trace, or relevant parts of a stack trace? Can you also confirm that you are using the latest version of Mapster?

I confirm this issue is occurring using the Mapster 7.3.0 Nuget package.

The behaviour when using a tuple with a single element matches my expectations. For instance:

source.Adapt<Dest>() returns null if source is null

(source).Adapt<Dest>() returns null if source is null

but when using multiple elements it throws an exception (even without a config specified)

(source1, source2).Adapt<Dest>() throws NullReferenceException if either source is null

I'm not sure what should happen if no config is specified, but certainly in my use-case I was expecting dest.Application to be null if src.Item3 is null

Yes! I have same problem with version 7.3.0

`config.ForType<(Pair?, Record?, Favorite?), PairDto>()

          .Map(dest => dest, src => src.Item1)

          .Map(dest => dest, src => src.Item2, srcCond => srcCond.Item2 != null)

          .Map(dest => dest, src => src.Item3, srcCond => srcCond.Item3 != null); `

A class as a reference type can always have a Null value.
NullableExpressionVisitor only checked for the presence of NullableAttribute.

It seems to be related to how nullability is determined for reference Tuple and ValueType members

(a, b, c) it is ValueTuple and Item3 has NullableAttribute [Nullable((byte) 1)] == not-null;

when you use reference Tuple
Tuple<a, b, c> Item3 does not get NullableAttribute at all

Which gave a false negative when checked in InvokerModel.
Because of this, the Condition was shortened to:

new Application()
{
Id = src.Item3.Id,
Name = src.Item3.Name
})