`#predicates_return(false)` breaks NullObject coercion

[nilcolor]

# without config.predicates_return false
NullObject = Naught.build do |config|
  def coerce(other)
    [0, other]
  end
end

null = NullObject.new;
1 / null # => 0

# with config.predicates_return false
NullObject = Naught.build do |config|
  config.predicates_return false

  def coerce(other)
    [0, other]
  end
end

null = NullObject.new;
1 / null # => NullObject can't be coerced into Fixnum