Problem with other wallet

When I go to my wallets, I get the following message: Échec du chargement des portefeuilles secondaires. Cannot read property 'substring' of null

I suspect some wallet has been incorrectly saved locally at some point. But this is actually blocking me when doing other actions (such as certifying someone), because it offers to choose the wallet with which to make the action, and the same error message blocks the next actions.

Cesium v1.4.2 installed on Ubuntu 16.