[Fix] Handle no matching output for Include Table group

[nguyen-v]

This PR fixes an error that was introduced with PR #707. When a group is defined with an output that is not given to the Include Table preflight, the following error was raised:

out, csv = out_to_csv_mapping.get(group_suffix)
    ^^^^^^^^
TypeError: cannot unpack non-iterable NoneType object

which is fixed by first checking if out_to_csv_mapping.get(group_suffix) is None.

[set-soft]

Hi @nguyen-v !
Please rebase the patch so it includes only the last commit.
Also: I think a better solution is to just use out, csv = out_to_csv_mapping.get(group_suffix, (None, None))

[nguyen-v]

Please rebase the patch so it includes only the last commit.
Also: I think a better solution is to just use out, csv = out_to_csv_mapping.get(group_suffix, (None, None))

Just rebased to dev with your suggestion