Fixed a few typos.
Improvements
Fixed indentation
Fix typo in Manager.php

s/their/there
Use data_get in Collection::valueRetriever
Dry up Facade very slightly
Enable dot notation for array_add
Merge pull request #4280 from Anahkiasen/dot-callback

Use data_get in Collection::valueRetriever
Use is_null.
Merge pull request #4256 from Marwelln/master

Fixed indentation
Fix conflicts.
Merge pull request #4222 from GrahamCampbell/4.1-stuff

[4.1] Improvements
Fixing conflicts and merge.