QuerySet.union() with queryset that raises EmptyResultSet results in an empty set

[Jon Dufresne]

Similar and followup to ticket #28293. Tested on Django 1.11.3.

As QuerySet.union() uses the SQL UNION operator, I would expect "SET1 UNION <EMPTY SET>" to result in SET1. If the empty set is the results of ​EmpytResultSet being raised, the .union() result is an empty set, not SET1.

Example test case:

>>> import django
>>> django.__version__
'1.11.3'
>>> from django.contrib.auth.models import User
>>> qs1 = User.objects.all() 
>>> qs1.count()
100
>>> qs2 = User.objects.filter(pk__in=[])
>>> qs2.count()
0
>>> list(qs1.union(qs2))
[]

[Mariusz Felisiak]

difference is also affected.

[Mariusz Felisiak]

I attached tests.