Is this the behaviour we want? is_valid function returns input variable

[eurunuela]

As I'm working on the unit tests, I've just seen that the is_valid function returns the input variable. Doesn't it make more sense for it to be a void function? If the variable is not valid, it could raise an error, but do nothing otherwise.

https://github.com/smoia/phys2bids/blob/f2d7d52e4e9d9d963f98aeb8809c81660e2f1794/phys2bids/physio_obj.py#L37

[smoia]

Now it's like that because it's used during the assignment of properties in the init of our objects.
At the moment, there's fewer cases for it to assign to void than for assign to a variable.
This said, it's true that before either your or @rmarkello 's review in #38 it returned something depending on an input parameter (return_val=True).
For me it's a way to put it in a pipe, and it can be extended if we need it later on in a similar way to keep the code neat.
I also understand the idea behind this issue, so although I prefer this way it's not a strong preference.