CGMES: Fix the export process for IIDM models without properties or aliases

[marqueslanauja]

Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• A PR or issue has been opened in all impacted repositories (if any)

Does this PR already have an issue describing the problem?

What kind of change does this PR introduce?

Bug fix.

What is the current behavior?

The CGMES exporter throws an exception when exporting models with two or more control areas and without aliases or properties.
The energyIdentCodeEic attribute of the control areas is exported empty, causing an exception when the exported model is re-imported

What is the new behavior (if this is a feature change)?

Both bugs have been fixed.

Does this PR introduce a breaking change or deprecate an API?

• Yes
• No

If yes, please check if the following requirements are fulfilled

• The Breaking Change or Deprecated label has been added
• The migration steps are described in the following section

What changes might users need to make in their application due to this PR? (migration steps)

Other information:

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud