Discrepancy in `DateTime` field value If the django orm union() is used with the empty array in the filter.

[Shashank Parekh]

class detail(models.Model):
      date_field = models.DateTimeField(null=True, index=True)
      guid = models.CharField(null=True, index=True)
      mobile = models.CharField(null=True, index=True)
      id = models.CharField(null=True, index=True)

p=detail.objects.filter(guid__in=[]).order_by('-date_field')
q=detail.objects.filter(mobile__in=['8970405058']).order_by('-date_field')
v = (p.union(q)).order_by('-date_field')
v[0].date_field   # Output is  '2018-10-08 12:51:39'.

For this case, instead of getting datetime value, getting the string value.

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p=detail.objects.filter(guid__in=['some_garbage_value']).order_by('-date_field')
q=detail.objects.filter(mobile__in=['8970405058']).order_by('-date_field')
v = (p.union(q)).order_by('-date_field')
v[0].date_field .  # Output is datetime.datetime(2018, 10, 8, 12, 51, 39)

If I don't pass the empty array in filtering then getting the DateTime value.

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p=detail.objects.filter(guid__in=['some_garbage_value']).order_by('-date_field')
q=detail.objects.filter(mobile__in=['8970405058']).order_by('-date_field')
v = (p.union(q))
v[0].date_field .  # Output is datetime.datetime(2018, 10, 8, 12, 51, 39)

If I pass the empty array but withour order_by clause then getting the DateTime value.

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There is a discrepancy in DateTime field value If the union is used with the empty array in the filter.