make sure abstract factories, factories and services all handle types consistently
Merge pull request #5293 from stefanotorresi/hotfix/5289

Fix #5289 (abstract factories return type)

Conflicts:
	tests/ZendTest/ServiceManager/ServiceManagerTest.php
[#5293] review

- do not call initializers if we have a null value
Merge branch 'hotfix/5293'

Close #5293
Fixes #5289