Refactor data source to throw exception instead of returning optionals

[staudtMarius]

Resolves #707

[sonatype-lift]

🛠 Lift Auto-fix

Some of the Lift findings in this PR can be automatically fixed. You can download and apply these changes in your local project directory of your branch to review the suggestions before committing.¹

# Download the patch
curl https://lift.sonatype.com/api/patch/github.com/ie3-institute/PowerSystemDataModel/712.diff -o lift-autofixes.diff

# Apply the patch with git
git apply lift-autofixes.diff

# Review the changes
git diff

Want it all in a single command? Open a terminal in your project's directory and copy and paste the following command:

curl https://lift.sonatype.com/api/patch/github.com/ie3-institute/PowerSystemDataModel/712.diff | git apply

Once you're satisfied commit and push your changes in your project.

Footnotes

1. You can preview the patch by opening the patch URL in the browser. ↩

[sebastian-peter]

Some more comments from my side :)

[sebastian-peter]

Ok, we got it done! Thanks a lot @staudtMarius for this contribution, I think this improves usability of PSDM a lot!