Fixed AnswerCall Attribute Of Ring BXML Verb

Changed the answerCall field of the Ring class from a boolean primitive to a Boolean wrapper for a default 'null' value if not explicitly set. Otherwise, the boolean primitive would default to 'true' and the attribute would be serialized as such, even if the value wasn't set. Also added a test to assert values that aren't set aren't serialized into the BXML.

src/main/java/com/bandwidth/voice/bxml/verbs/Ring.java

@@ -25,5 +25,5 @@ public class Ring implements Verb {
      * incoming call. Default value is 'true'.
      */
     @XmlAttribute
-    private boolean answerCall;
+    private Boolean answerCall;
 }

src/test/java/com/bandwidth/BxmlTest.java

@@ -165,7 +165,7 @@ public void testNestedGatherMultipleVerbs() {
 
         assertEquals("BXML strings not equal", expected, response);
     }
-    
+
     @Test
     public void testNestedGatherSingleVerb() {
         SpeakSentence speakSentence = SpeakSentence.builder()
@@ -442,6 +442,16 @@ public void testRing() {
         assertEquals("BXML strings not equal", expected, response);
     }
 
+    @Test
+    public void testRingDefault() {
+        Ring ring = Ring.builder().build();
+        String response = new Response().add(ring).toBXML();
+
+        String expected = "<?xml version=\"1.0\" encoding=\"UTF-8\"?><Response><Ring/></Response>";
+
+        assertEquals("BXML strings not equal", expected, response);
+    }
+
     @Test
     public void testStopGather() {
         StopGather stopGather = StopGather.builder().build();