Commit 3dbedd2 added NOT NULL constraints both to table creation and modification. For creation the new default makes sense, but the generic situation for changing a table is that there exist records. Those records have no creation or modification timestamps, and in the general case you don't even know them, so when updating a table these constraints are not going to work. See a bug report for this use case in #3334.
* master-security: Ensure  respects the status of the buffer. delete vulnerable AS::SafeBuffer# use AS::SafeBuffer#clone_empty for flushing the output_buffer add AS::SafeBuffer#clone_empty fix output safety issue with select options Conflicts: actionpack/lib/action_view/helpers/tags/base.rb
This reverts commit 1b9e19c.