Skip removing validations if none are added

Fixes ice-cube-ruby#281

Author: avit

lib/ice_cube/validations/day.rb

@@ -5,6 +5,8 @@ module IceCube
   module Validations::Day
 
     def day(*days)
+      days = days.flatten
+      return self if days.empty?
       days.flatten.each do |day|
         unless day.is_a?(Fixnum) || day.is_a?(Symbol)
           raise ArgumentError, "expecting Fixnum or Symbol value for day, got #{day.inspect}"

spec/examples/weekly_rule_spec.rb

@@ -102,6 +102,14 @@ module IceCube
       expect { schedule.add_recurrence_rule Rule.weekly.day(["1", "3"]) }.to raise_error
     end
 
+    it 'should ignore weekday validation when no days are specified' do
+      schedule = Schedule.new(t0 = WEDNESDAY)
+      schedule.add_recurrence_rule Rule.weekly(2).day([])
+
+      times = schedule.occurrences(t0 + 3 * ONE_WEEK)
+      expect(times).to eq [t0, t0 + 2 * ONE_WEEK]
+    end
+
     it 'should produce the correct number of days for @interval = 2 with only one day per week' do
       schedule = Schedule.new(t0 = WEDNESDAY)
       schedule.add_recurrence_rule Rule.weekly(2).day(:wednesday)