I am trying to search a column (C5:C400) to find out when it runs to a null
value, then search down a different column (G) starting from that same row
and return the first positive number found.

Can anyone help? I've been using the following as a starting point, but I'm
stuck on how to complete it.

=INDEX(MATCH(TRUE,G5:G4000),MATCH(TRUE,C5:C400=0, 0))

Thanks!