assign_attributes should return if argument is blank.

If you are passed an empty hash, then assign_attributes doesn't need to
do any work and can just return early. This should fix the failing Agile
Web Development tests.
push preloaded test up to the factory method so we can eliminate
conditionals from the individual preloaded classes
eliminate the `loaded?` conditional
all records have a preloaded, so eliminate that conditional
eliminate unused ivar
Use the given name in html_options for the hidden field in collection_check_boxes
[Documentation] Add a missing validation to I18n docs

The guide was missing a description of the error message
interpolation for validates_numericality_of with
the :only_integer option.
guarantee that `klass` is not nil inside the preloader objects
Fix typo in number_to_human docs: you -> your
Merge pull request #12347 from macmartine/master

Fix typo in number_to_human docs: you -> your
Merge pull request #12341 from odigity/master

added column type to example in section 2.3
Merge pull request #12346 from graysonwright/patch-1

[Documentation] Add a missing validation to I18n docs
Merge pull request #12343 from wangjohn/fix_failing_agile_controller_tests

assign_attributes should return if arguments are blank
Add regression test to #12343
Merge pull request #12344 from angelic/collection_check_boxes_with_name

Use the given name in html_options for the hidden field in collection_ch...
Add CHANGELOG entry for #12344

[ci skip]
push slice loading to it's own method so we can remove the type casting
code
added "id: false" to HABTM join table example

Based on the instructions further down in section 3.3.2.
Getting Started Guide: Hello Rails! -> Hello, Rails! and wrap code tag
Merge pull request #12351 from francisgo/patch-2

Getting Started Guide: Hello Rails! -> Hello, Rails! and wrap code tag