Found nothing at all here but it's not important (2,6)
I believe the answer is:
no matter
'it's not important' is the definition.
(I've seen this before)
'found nothing at all here' is the wordplay.
I cannot really see how this works, but
'nothing' could be 'no' (similar in meaning) and 'no' is found in the answer.
'at' is within the answer.
This may be the basis of the clue (or it may be nonsense).
'but' acts as a link.
Can you help me to learn more?
(Other definitions for no matter that I've seen before include "What about it, it's unimportant" , "It's not important - what a torment" , "Never mind" , "It's of little consequence - what a torment" , "Who cares" .)