cubicweb-wsme #5662553 Crash if an entity type does not exist [done]

If a webservice type refers to a non-existing entity type, the cube crashes when loading, which makes it impossible to run the migration scripts.

prioritynormal
typebug
done in0.2.2
load left0.000
closed by#1b2b39a1afe6 Avoid a crash if an entity type does not exist
patchDon't crash if a rtype does not exist [applied]Avoid a crash if an entity type does not exist [applied]