Prevent ontoconvert from crashing when the --iri option is given

[jesper-friis]

Description

Prevent ontoconvert from crashing unintentionally when the --iri option is given.

Include also some minor code cleanup.

Type of change

• Bug fix.
• New feature.
• Documentation update.
• Test update.

Checklist

This checklist can be used as a help for the reviewer.

• Is the code easy to read and understand?
• Are comments for humans to read, not computers to disregard?
• Does a new feature has an accompanying new test (in the CI or unit testing schemes)?
• Has the documentation been updated as necessary?
• Does this close the issue?
• Is the change limited to the issue?
• Are errors handled for all outcomes?
• Does the new feature provide new restrictions on dependencies, and if so is this documented?

Comments

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.05%. Comparing base (65e2b6c) to head (00ec1b7).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #902   +/-   ##
=======================================
  Coverage   73.05%   73.05%           
=======================================
  Files          19       19           
  Lines        3919     3919           
=======================================
  Hits         2863     2863           
  Misses       1056     1056           

Flag	Coverage Δ
unittests	73.05% <100.00%> (ø)

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