calling Add on a ManyToMany field with empty arguments results in bad SQL

[carl.shimer@…]

Scenario:

You have generic code which wants to add one or more entries to a ManyToMany field. the easy way to do this is something like this:

mapping_values = Model_one.object.all.filter(foo__bar__baz__in=mylistcriteria)
exising_object.manytomanyfield.add(*mapping_values)

if mapping fields is empty,e.g [] this will result in an exception because of bogus SQL generation.
calling add with empty args should probably do nothing rather than throwing an exception. Of course,this is easy to code around with a simplecheck.

[Russell Keith-Magee]

Duplicate of #2473.