Check if the solution variables content is not None

[pepeleduin]

When running pytest there is a TypeError: unsupported operand type(s) for -: 'NoneType' and 'int'. This is because there is no checking of the content of variables before doing operations with integers.

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[pchtsp]

thanks, can you sign the license?

[pepeleduin]

Done!

[pchtsp]

I think you should raise a PulpError if the variable has the value None, because it should fail. With your current modification the test would pass when v.varValue is None.