Use credentials IsEmpty again

[polldo]

Motivation

There is a nasty leftover: I changed the name of credentials IsEmpty method without changing its logic.
Also, we actually need to know if the credentials config file has any mandatory parameter or not. Thus, the name IsEmpty fits better this need.

Change description

Put back the old IsEmpty name.

Additional Notes

Reviewer checklist

• PR address a single concern.
• PR title and description are properly filled.
• Changes will be merged in main.
• Changes are covered by tests.
• Logging is meaningful in case of troubleshooting.
• History is clean, commit messages are meaningful (see CONTRIBUTING.md) and are well formatted.

[rsora]