No I18n::MissingInterpolationArgument when no arguments are passed

[danielpoonwj]

What I tried to do

Content of config/locales/en.yml:

en:
  greeting: Hello %{first_name} %{last_name}

Calling I18n without arguments or with an empty argument hash does not raise I18n::MissingInterpolationArgument, but just passes the original string as-is.

[1] pry(main)> I18n.t('greeting')
=> "Hello %{first_name} %{last_name}"

[2] pry(main)> I18n.t('greeting', {})
=> "Hello %{first_name} %{last_name}"

What I expected to happen

Consistency in behaviour when passing incomplete interpolation arguments, since passing no arguments should fall under missing interpolation arguments.

[1] pry(main)> I18n.t('greeting', first_name: 'John')
I18n::MissingInterpolationArgument: missing interpolation argument :last_name in "Hello %{first_name} %{last_name}" ({:first_name=>"John"} given)

[2] pry(main)> I18n.t('greeting', last_name: 'Doe')
I18n::MissingInterpolationArgument: missing interpolation argument :first_name in "Hello %{first_name} %{last_name}" ({:last_name=>"Doe"} given)

[3] pry(main)> I18n.t('greeting', middle_name: 'Danger')
I18n::MissingInterpolationArgument: missing interpolation argument :first_name in "Hello %{first_name} %{last_name}" ({:middle_name=>"Danger"} given)

Do let me know if it's intended behaviour or if it could potentially be due to the configuration of my project.

Versions of i18n, rails, and anything else you think is necessary

i18n (1.7.0)

[radar]

This is an intentional behaviour of the library, and explained here: https://github.com/ruby-i18n/i18n/blob/master/lib/i18n/tests/interpolation.rb#L6-L18