Hi everyone
Not sure if anyone else uses this, but we have a serious use case, where we would like to use FluentAssertions within Expression<> trees.
Generally, it shouldn't be a problem, but the use of default values in method calls is not allowed inside Expression trees.

GetTheTree(items => items.Should().Contain(x => x.FirstName == "Name"));

Results in a CS0854: An expression tree may not contain a call or invocation that uses optional arguments.
It is due to the optional arguments in Contain(..., string because = "", params object[] becauseArgs)

I see two possible solutions that both have severe downsides:

1. Rather than relying on default values, use method overloads. This would require 2 extra method per supported assertion. Yikes, but probably the cleanest way to support Expression trees.
2. As a workaround we call the assertion like so:
   GetTheTree(items => items.Should()**._()**.Contain(x => x.FirstName == "Name"))

After the Should(), we are using the _() to wrap the various Assertion types in our own class, where we can then place new versions of the different methods that do not use default values.

That's also not a nice solution and we would have to define all the overloads to use everything.

Does anyone know a better way around this?