Before this change missing timezone data for any of the time zones
defined in `ActiveSupport::Timezone::MAPPING` caused a `comparison of
NilClass with ActiveSupport::TimeZone failed` exception.
Attempting to get a timezone by passing a number/duration to `[]` or
calling `all` directly will try to sort sort the values of `zones_map`.
Those values are initialized by the return value of `create(zonename)`
which returns `nil` if `TZInfo` is unable to find the timezone
information.
In our case the exception was triggered by an outdated tzdata package
which did not include information for the "recently" added time zones.
Before 078421bacb `zones_map` only
returned the information that have been loaded into `@lazy_zone_map`
which ignored time zones for which the data could not be loaded, this
change restores the previous behaviour.
In Ruby 2.4 the `to_time` method for both `DateTime` and `Time` will
preserve the timezone of the receiver when converting to an instance
of `Time`. Since Rails 5.0 will support Ruby 2.2, 2.3 and later we
need to introduce a compatibility layer so that apps that upgrade do
not break. New apps will have a config initializer file that defaults
to match the new Ruby 2.4 behavior going forward.
For information about the changes to Ruby see:
https://bugs.ruby-lang.org/issues/12189https://bugs.ruby-lang.org/issues/12271Fixes#24617.
