Improved an error message
Improved an error message


Former-commit-id: e6e35d96837464cc97dd408be133b957e052fb34 [formerly de7abaf2393bac7855fcc30173cd011985d7284d]
Former-commit-id: 0d8c5d2602fa63b3d79dff5dacc8d7a0bd53c2cf
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine