Remove empty lists froms lists at any level in R

I have a list that have several list inside it:

> res$go $MF $MF[[1]] term evidence id pubmed 1 G-protein coupled receptor activity IEA GO:0004930 NA 2 calcium ion binding IEA GO:0005509 NA 3 protein binding IPI GO:0005515 17474147 $MF[[2]] NULL $BP $BP[[1]] term evidence id pubmed 1 neuron migration IEA GO:0001764 NA 2 regulation of protein phosphorylation IEA GO:0001932 NA 3 homophilic cell adhesion via plasma membrane adhesion molecules IEA GO:0007156 NA 4 G-protein coupled receptor signaling pathway IEA GO:0007186 NA 5 axonal fasciculation IEA GO:0007413 NA 6 regulation of protein localization IEA GO:0032880 NA 7 cilium assembly IEA GO:0042384 NA 8 Wnt signaling pathway, planar cell polarity pathway NAS GO:0060071 24431302 $BP[[2]] NULL $CC $CC[[1]] term evidence id 1 plasma membrane IEA GO:0005886 2 integral component of membrane IEA GO:0016021 $CC[[2]] NULL 

However, some of them have NULL lists within them. I was trying to find a way to remove empty lists at these levels from my res$go list but I couldn't.

I tried:

res$go[!is.null(res$go)]

But the results were the same, even if I try specifying a level further I can't remove them.

res$go$BP[!is.null(res$go$BP)]

Thanks for the help.

OUTPUT from dput

> dput(res$go) structure(list(MF = list(structure(list(term = c("G-protein coupled receptor activity", "calcium ion binding", "protein binding"), evidence = c("IEA", "IEA", "IPI"), id = c("GO:0004930", "GO:0005509", "GO:0005515" ), pubmed = c(NA, NA, 17474147L)), .Names = c("term", "evidence", "id", "pubmed"), class = "data.frame", row.names = c(NA, 3L)), NULL), BP = list(structure(list(term = c("neuron migration", "regulation of protein phosphorylation", "homophilic cell adhesion via plasma membrane adhesion molecules", "G-protein coupled receptor signaling pathway", "axonal fasciculation", "regulation of protein localization", "cilium assembly", "Wnt signaling pathway, planar cell polarity pathway" ), evidence = c("IEA", "IEA", "IEA", "IEA", "IEA", "IEA", "IEA", "NAS"), id = c("GO:0001764", "GO:0001932", "GO:0007156", "GO:0007186", "GO:0007413", "GO:0032880", "GO:0042384", "GO:0060071"), pubmed = c(NA, NA, NA, NA, NA, NA, NA, 24431302L)), .Names = c("term", "evidence", "id", "pubmed"), class = "data.frame", row.names = c(NA, 8L)), NULL), CC = list(structure(list(term = c("plasma membrane", "integral component of membrane"), evidence = c("IEA", "IEA"), id = c("GO:0005886", "GO:0016021")), .Names = c("term", "evidence", "id"), class = "data.frame", row.names = 1:2), NULL)), .Names = c("MF", "BP", "CC"))