Fix https://github.com/ControlSystemStudio/phoebus/issues/3685

[lcaouen]

Fix #3685

• Testing:
  • unit test PreferencesReaderTest.testListSettings runs successfully

[shroffk]

So now
allKeysWithPackages.get("org.phoebus.ui/excluded_packages_from_settings_check");

could return a null while previous it would only return empty strings?

[lcaouen]

So now allKeysWithPackages.get("org.phoebus.ui/excluded_packages_from_settings_check");

could return a null while previous it would only return empty strings?

allKeysWithPackages is a Map so the get method returns null if this map contains no mapping for the key.
When you run the JUnit tests no property files are loaded so the map is empty and the key cannot be found.