When an nt:folder node is present under an orderable node, the "jackrabbit-emptyelements" validator will report an issue (breaking the build with the default settings of the package Maven plugin). I believe this shouldn't be reported as an issue because the AEM Package Manager can generate packages like this. For example, see the attached test.zip file, which was exported on an out-of-the-box AEM 6.5 instance with dummy nodes.
To reproduce, save test.zip somewhere, then invoke the validation Maven goal in the command like like this:
mvn org.apache.jackrabbit:filevault-package-maven-plugin:validate-package -Dvault.packageToValidate=test.zip
test.zip contains the following very simple node hierarchy:
The error I'm getting is:
[ERROR] ValidationViolation: "jackrabbit-emptyelements: Found empty nodes: '/test/foo' (in 'test\.content.xml') (used for ordering only) which are included in the filter with mode=merge. Rather use the according include/exclude patterns."