There is a field typename in the nodes table in the database, which (despite its name) is an integer that indicates whether the node is a note, a corpus, etc. The correspondence between this integer and a value of Haskell type NodeType is made in the nodeTypes declaration in module Gargantext.Database.Admin.Config.

It is conceivable for a node to be stored as a row in the nodes table without its typename field corresponding to any NodeType value. A constructor of NodeError should be added to handle this case (and all of the related machinery should be updated accordingly).