module Ransack::Configuration

end
config.default_predicate = 'eq'
# Use the 'eq' predicate if an unknown predicate is passed
Ransack.configure do |config|

like `config/initializers/ransack.rb` as follows:
a default predicate by setting it in an initializer file
By default Ransack ignores empty predicates. Ransack can also fallback to

def default_predicate=(name)
  self.options[:default_predicate] = name
end