As an example if there are projects with values `a`, `b` and one without a value, should they be ordered like that or project without a value should be before those with values `a` and `b`? Default db behaviour is to put one without a value at the end, current behaviour for custom fields of most formats is to put it at the beginning. It may be a way to make ordering of empty string values and empty values consistent, which can be solved other way too. It is also different between projects and working packages:

For projects:
Absent values are sorted before rest for `text`, `link`, `date`, `boolean`, `list` (only when multi value is allowed), 
Absent values are sorted after rest for `integer`, `float`, `list` (only when multi value is not allowed), `user`, `version`

For work packages:
Absent values are sorted before rest for `text`, `link`, `integer`, `float`, `date`, `boolean`, `list` (only when multi value is allowed)
Absent values are sorted after rest for `list` (only when multi value is not allowed), `user`, `version`

### Acceptance criteria:

* When ordering ascending by any custom field, items without value should precede items with value/values

* When ordering descending, items without value should follow items with value/values

* Custom fields with format `boolean` currently display Begin of the insertiondefaultEnd of the insertion Begin of the deletion unsetEnd of the deletion value Begin of the insertionif it is unsetEnd of the insertion Begin of the deletion as `no`End of the deletion