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`, Begin of the insertion`list` (only when multi value is not allowed),End of the insertion `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 Begin of the insertionfor `list` (only when multi value is not allowed), `user`,End of the insertion Begin of the deletion for `user`,End of the deletion `version`