Bug/57401 sorting by link custom field causes exception

[toy]

Ticket

OP#57401

What are you trying to accomplish?

Allow ordering by custom field of link format

What approach did you choose and why?

Adding sorting as for string format + add tests for ordering by custom fields of all formats

Merge checklist

• Added/updated tests
• Added/updated documentation in Lookbook (patterns, previews, etc)
• Tested major browsers (Chrome, Firefox, Edge, ...)

[ulferts]

🙇 for adding all the specs.

The functionality is also fine and works as expected.

What I have been wondering about though, is that the specs are currently work package Query specific. The same code is however also used in the ProjectQuery and there the order statement are included in a different manner. From my point of view it would help to copy over the specs to the ProjectQuery realm as well. That would in my expectation also make the subsequent changes to be carried out for the optimization of the performance a safer change. But this needn't be done in this PR necessarily.

[toy]

True, also it looks like only for work packages there is a logic to change the placement of null values (null_handling method). I'll create a maintenance ticket for that.