Fix OmegaConfigLoader when file is empty

[noklam]

NOTE: Kedro datasets are moving from kedro.extras.datasets to a separate kedro-datasets package in
kedro-plugins repository. Any changes to the dataset implementations
should be done by opening a pull request in that repository.

Description

Currently, if you have an empty configuration file with OmegaConfigLoader, you will get this error which isn't very accurate.

This draft PR is just a starting point, it's expected to be picked up by someone and worked on it further.

            raise MissingConfigException(
                f"No files of YAML or JSON format found in {base_path} or {env_path} matching"
                f" the glob pattern(s): {[*self.config_patterns[key]]}"
            )

Possible Alternative

• Refactor the code and eliminate the need of handling it with a special condition. The code below shows that we cannot differentiate between missing and empty configs.
• If this is necessary, we should at least provide a better message (Which I think it shouldn't be, as we don't need this for the other ConfigLoader).

Lines 276-277 don't actually cause a bug I think, so if removing them makes some tests fail and it seems related to #2556 then let's leave those here for now and try to remove them in that PR.

kedro/kedro/config/omegaconf_config.py

Lines 274 to 275 in 807c4e6

	if not aggregate_config:
	return {}

We should also take this as an opportunity to revisit the logic and see if we can simplify it

Development notes

Checklist

• Read the contributing guidelines
• Opened this PR as a 'Draft Pull Request' if it is work-in-progress
• Updated the documentation to reflect the code changes
• Added a description of this change in the RELEASE.md file
• Added tests to cover my changes

[noklam]

Found this issue while writing test for #2467 @merelcht for comments.

[merelcht]

Good find. I agree that ideally it shouldn't throw an error at all but just return an empty dict.

[noklam]

Close in favour of #2566, need more work on revisiting the load_and_merge logic.