Handle null and empty lines

[wallymathieu]

[andyfeller]

Thanks for the contribution, @wallymathieu! 🎉 If I can ask for my own understanding, what kind of situation arose that required these changes being needed?

From all appearances this seems like a simple change that I'm all to happy to accept, I just want to consider whether any additional changes are necessary.

[wallymathieu]

Mostly it was to try out this project. I got some errors and wanted to get fewer null reference exceptions while entering for instance invalid input.