Optimize DiscountBudget for month lookups

lib/planet_express/discounts/discount_budget_for_month_repository.rb

@@ -6,29 +6,16 @@ module PlanetExpress
     attr_reader :data
 
     def initialize(data: {})
-      @data = data
+      @data = Hash.new do |hash, key|
+        hash[key] = DiscountBudget.new(budget: DEFAULT_BUDGET)
+      end.merge(data)
     end
 
     def for_month(date)
-      return budget_for_month(date) if budget_for_month?(date)
-
-      add_budget_for_month(date)
-      budget_for_month(date)
-    end
-
-    private
-
-    def budget_for_month(date)
       data[start_of_month(date)]
     end
 
-    def budget_for_month?(date)
-      !budget_for_month(date).nil?
-    end
-
-    def add_budget_for_month(date)
-      data[start_of_month(date)] = DiscountBudget.new(budget: DEFAULT_BUDGET)
-    end
+    private
 
     def start_of_month(date)
       Date.new(date.year, date.month, 1)