v4.1.0

Bug fixes

• Fix validate_uniqueness_of so that it works when a scope is defined as a
  string instead of a symbol on the model. (#1176)
• Fix have_db_index so that it can be used against multiple models that are
  connected to different databases. (#1200)

Features

• Add support for Rails 6. No new Rails 6 features are supported, but only
  existing features that broke with the upgrade. (#1193)
• Add support for expression indexes (Rails 5, Postgres only) to
  have_db_index. (#1211)
• Add allow_nil to the validate_presence_of matcher. (834d8d0, #1100)

Improvements

• Update validate_presence_of so that if it is being used against an
  association which is required: true or optional: false, or it is not
  configured as such but ActiveRecord defaults belong_to associations to
  optional: false, and the matcher fails, the developer is reminded in the
  failure message that the belong_to matcher can be used instead. (#1214,
  8697b01)
• Update define_enum_for so that it produces a more helpful message on
  failure. (#1216)