Don't skip interpolate for the empty values.

[piecehealth]

The I18n.t method won't raise I18n::MissingInterpolationArgument error if the given options are empty, which is not as expected.

e.g.

en:
    greeting: "Hello %{firstname} %{lastname}"

I18n.t("greeting", firstname: "Michael", lastname: "Jordan") # => "Hello Michael Jordan"
I18n.t("greeting") # => "Hello %{firstname} %{lastname}"
I18n.t("greeting", firstname: "Michael") # => I18n::MissingInterpolationArgument