Allow credit cards to be specified as month/year instead of date

lib/fake_braintree/customer.rb

@@ -30,9 +30,10 @@ def customer_hash
         if !hash["credit_card"].empty?
           hash["credit_card"]["last_4"]           = hash["credit_card"].delete("number")[-4..-1]
           hash["credit_card"]["token"]            = md5("#{hash['merchant_id']}#{hash['id']}")
-          expiration_date = hash["credit_card"].delete("expiration_date")
-          hash["credit_card"]["expiration_month"] = expiration_date.split('/')[0]
-          hash["credit_card"]["expiration_year"]  = expiration_date.split('/')[1]
+          if expiration_date = hash["credit_card"].delete("expiration_date")
+            hash["credit_card"]["expiration_month"] = expiration_date.split('/')[0]
+            hash["credit_card"]["expiration_year"]  = expiration_date.split('/')[1]
+          end
 
           credit_card = hash.delete("credit_card")
           hash["credit_cards"] = [credit_card]

spec/fake_braintree/customer_spec.rb

@@ -1,7 +1,9 @@
 require 'spec_helper'
 
 describe "Braintree::Customer.create" do
-  let(:expiration_date) { "04/2016" }
+  let(:expiration_month) { "04" }
+  let(:expiration_year)  { "2016" }
+  let(:expiration_date)  { [expiration_month, expiration_year].join("/") }
   after { FakeBraintree.verify_all_cards = false }
 
   def create_customer_with_credit_card(options)
@@ -14,6 +16,13 @@ def create_customer_with_credit_card(options)
     result.should be_success
   end
 
+  it "creates a customer using an expiration month and year" do
+    result = create_customer_with_credit_card(:number => TEST_CC_NUMBER,
+                                              :expiration_month => expiration_month,
+                                              :expiration_year => expiration_year)
+    result.should be_success
+  end
+
   it "records the billing address" do
     result = create_customer_with_credit_card(
       :number => TEST_CC_NUMBER,