How to reproduce it :

In workflows.xml declare 2 models :

<workflow name="bpm-default" type="file" location="bpm/workflow-bpm-default.xml"/>
<workflow name="bpm-test" type="file" location="bpm/workflow-bpm-test.xml"/>

The second one is missing into the bpm folder

In the CMS, the 2 models are proposed and if I try to use the second one, an error occurs.

Expected behavior :
If the definition of the model is missing, it should not appears in the list od valid models.