Unclear Error on yml with non-existing class

[jasperfennet]

When adding a non-existing class to the yml the error generated is unclear.

when adding the following to an enun.{locale}.yml
non-existing_class: 'FooBar'

the error message states
Could not load constants for a class ''

Where the actual cause is
Could not load constants for non-existing class 'non-existing_class'
or
Class 'non-existing_class' does not exists