Proper error message for non-existing OEO class

[l-emele]

Description of the issue

When one opens the IRI of a non-existent OEO class/individual/property, e.g. https://openenergyplatform.org/ontology/oeo/OEO_99999999/ then an almost empty page is shown:

The user does not get any feedback that she or he requested a non-existing entity.

Ideas of solution

Ontobee is a good example how to handle this: For a non-existent IRI the user gets a delievered a proper error message. For example, http://purl.obolibrary.org/obo/BFO_1234567 gets as usual¹ redirected to https://ontobee.org/ontology/BFO?iri=http://purl.obolibrary.org/obo/BFO_1234567 but it has the following content:

Workflow checklist

• I am aware of the workflow in CONTRIBUTING.md

Footnotes

1. OBO IRIs always redirect to Ontobee ↩

[jh-RLI]

A check has been added that now prevents the empty page from being displayed. It checks if the class name is available. Only the general 404 page is displayed. A more precise 404 page would be better, but I can't do it now :/

[l-emele]

I think a 404 page is sufficient at the moment.