If javax.lang.model.element.ModuleElement represents unnamed module which contains unnamed package then
ModuleElement.getEnclosedElements() returns empty list.

The minimized testcase is attached. In order to reproduce it, please:
1. Unzip attached archive on some Unix/Linux machine to a directory, say A.
2. Modify A/Test23/test.sh by setting JDK_HOME environment variable to your JDK installation.
3. Run A/Test23/test.sh.

On JDK9b127 this causes following output:

Root class: Test23
Root class package: unnamed package
Root class package module: unnamed module
Module 'unnamed module' packages number: 0