fix(check_report): Do not allow empty values

[jfagoagas]

Description

Do not allow empty values the mandatory values of a finding. We want to raise an exception if some value is not present.

Checklist

• Are there new checks included in this PR? Yes / No
  • If so, do we need to update permissions for the provider? Please review this carefully.
• Review if the code is being covered by tests.
• Review if code is being documented following this specification https://github.com/google/styleguide/blob/gh-pages/pyguide.md#38-comments-and-docstrings
• Review if backport is needed.
• Review if is needed to change the Readme.md

License

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.