Yes, even if you write « 0 » in the column « traitements et salaires » or if the amount you write is very small, do it. It's important.
In a few months, when other people receive a « avis d'imposition », you will receive a « avis de non imposition » on which will be written you must pay « 0 euros ».
This « avis de non imposition » is important, keep it. If you have children, you'll be entitled to reductions thanks to this document. If you want a loan or a mortgage, you might also have a special one thanks to this « avis de non imposition ».
And if you receive money from the "CAF" (caisse d'allocations familiales) they'll use your
"déclaration de revenus" to decide you much money you'll get next year. So, if you do not "déclarer vos revenus", at the end of this year, you won't receive anymore money from your