Fix: non primitive out types

[thinkbeforecoding]

This is a fix for non primitive out types in stored procedures.

I had a case with a output parameter of type Guid, the type provider could not use the Expr.Value(Activator.CreateInstance(…)) since it can do so only for primive types.
In the case of a non primite type, we use Expr.DefaultValue(t) which calls the default ctor.

The change in SetRef<'t> was necessary to set the output value to default<'t> when the parameter value is actually DBNull. This raise the question of actually making it optional…

[smoothdeveloper]

@thinkbeforecoding thanks for reporting the issue / fix.

Could you add a non regression test and a comment around the added check with a bit of context?

[thinkbeforecoding]

For the tests, I added a storedproc that pass or not the input Guid to out parameter depending on a bool parameter.
There is a tests where it's called with true, to check that everything is ok when there is a value, and a test with false to test when the out parameter is not set.

[thinkbeforecoding]

Is it ok like this ?

[thinkbeforecoding]

No prb, I pushed a version to our local nuget feed.
Thx !!