Invalid input for FacetFilters breaks repository

Invalid input like:

project:title!=

completely breaks repository, we should do some input validations and either skip invalid facet setup or throw/log some errors, but let repository to function so error can be fixed without re-deployment/server restart.

Addendum by aschrijvers : In this case it fails to load the specific faceted navigation node. However if the faceted navigation node is directly below the root , the entire repository becomes inaccessible since loading the children of the root node fails. If the broken faceted navigation node is nested in a deeper location, only that node is broken. However very annoying that the node cannot be fixed in running repository since the node cannot be loaded. This should be fixed