env_fetch.rb

require 'active_support'
require 'active_support/core_ext/object/blank'

def fetch(key, default: nil, scope: :rails)
  value = fetch_with_scope(key, scope, default: default)
  value.presence || raise(KeyError, "value for key #{key} cannot be blank")
end

def fetch_with_scope(key, scope, default: nil)
  ENV.fetch("#{scope.to_s.upcase}_#{key}") do
    ENV.fetch(key, *default)
  end
end