to reproduce :

• create a multi-configuration job, use slave axe
• unselect "master" (sole node) from axe
• save job configuration

=>
Failed to instantiate class hudson.matrix.LabelAxis from

{"kind":"hudson.matrix.LabelAxis","name":"label","stapler-class":"hudson.matrix.LabelAxis"}

"values" is missing from JSON data.
For sure, disabling all nodes from slave-axe don't make much sense, but this error is confusing for user.