These words: нечего, некогда, негде, некого
in which way they are distinguished from the usual words: ничего, никогда, нигде, никого.
For example in the dictionary for нечего and ничего it says Отрицательное местоимение.
So I conclude the every couple from the two sets of words grammatically has the same use.
I suppose they have a difference regarding the meaning