Error during import with mandatory property

Question

The customer has an issue with the import of his site.
The error is the following one:
 

Failed validation extranetSSM.zip/live-repository.xml validated in 396 ms
[...]
[Property [j:target] is mandatory but has no value

Cause

The content /sites/extranetSSM/home/newsletter-abonnements/corps/abonnement-newsletter where j:target property is missing a jnt:newsLetterSubscription type and must be referring to a jnt:newsLetter content in its j:target property.

Solution

The customer has updated the content of the type jnt:newsLetterSubscription in his own template.