Translation:My brother opened the wardrobe, but there was nothing there.
не было there wasn't
Then you remove the double negative.
I don't understand the construction" но там ничего не было". It's literally but there nothing it was not. How does it translate to "but there was nothing there"
Ничего не + verb is a very common structure in russian, used to express that the object of the verb is 'nothing' . In this case the verb is 'было' (there was) so 'ничего не было' translates to 'there was nothing'.
Everything has to be negated so double and triple negatives are a necessary function if the grammar structure.
Ничего = nothing and никогда = never.
Я никогда ничего не забывал = I never forgot nothing
P.S. I know that this phrase is used with the word "anything", not "nothing", but I wrote it like a mnemonic thing.