On several instances, among which dev we have an error message when sorting documents by occurence

For instance here : https://dev.sub.gargantext.org/#/share/NodeCorpus/188099

@karenkonou @AlfredoDiNapoli : I am not sure that's a purescript pb, so do not hesitate to change the project affectation @glocqueville @yacourt @fmaniere : for information as we need that functionality to be up for training as it is in the workflow for creating a good graph