In the feature selection stage, no feature is selected.

In the feature selection stage, no feature is selected,  and an error was returned:

`07-11 13:49:59 I hypernets.e.compete.py 882 - feature_selection drop 10 columns, 0 kept`

`    raise ValueError("No data output, ??? ")
ValueError: No data output, ??? `

Can **protection mechanism** be added so that at least a few features are retained when `selected` is None?
