can update_recurring_donation with a status_message nil (#57)

---------

Co-authored-by: Taylor Brooks <[email protected]>

lib/rock_rms/resources/recurring_donation.rb

@@ -73,7 +73,7 @@ def update_recurring_donation(
         options['EndDate']                  = end_date if end_date
         options['Summary']                  = summary if summary
         options['Status']                   = status if status
-        options['StatusMessage']            = status_message if status_message
+        options['StatusMessage']            = status_message if status_message || status_message == ''
 
         patch(recurring_donation_path(id), options)
       end

spec/rock_rms/resources/recurring_donation_spec.rb

@@ -66,6 +66,25 @@
       expect(resource).to be_nil
     end
 
+    it 'updates status_message with nil' do
+      expect(client).to receive(:patch)
+        .with(
+          'FinancialScheduledTransactions/123',
+          {
+            'NextPaymentDate' => '2018-01-01',
+            'StatusMessage' => ''
+          }
+      ).and_call_original
+
+      resource = client.update_recurring_donation(
+        123,
+        next_payment_date: '2018-01-01',
+        status_message: ''
+      )
+
+      expect(resource).to be_nil
+    end
+
     context 'arguments' do
       it 'require `id`' do
         expect { client.update_recurring_donation }