Provide a default Application

In case the user don't care :)

Fixes #7

README.md

@@ -28,6 +28,8 @@ Get a notifier:
         .initNotifier();
 ```
 
+The `application` is not mandatory, you'll get a default one if it's not set.
+
 Then send notification:
 
 ```java

send-notification/src/main/java/fr/jcgay/notification/SendNotification.java

@@ -10,6 +10,7 @@
 import java.util.Properties;
 import java.util.Set;
 
+import static com.google.common.base.Preconditions.checkNotNull;
 import static org.slf4j.LoggerFactory.getLogger;
 
 /**
@@ -38,9 +39,13 @@ public class SendNotification {
     private final NotifierProvider provider;
 
     private ConfigurationReader configuration;
-    private Application application;
     private ChosenNotifiers chosenNotifiers;
     private Properties additionalConfiguration;
+    private Application application = Application.builder()
+        .id("application/x-vnd-jcgay.send-notification-default")
+        .name("Send Notification (Default)")
+        .icon(Icon.create(SendNotification.class.getResource("/brochure5.png"), "send-notification"))
+        .build();
 
     SendNotification(ConfigurationReader configuration, OperatingSystem currentOs) {
         this(configuration, new NotifierProvider(currentOs));
@@ -87,7 +92,7 @@ public Notifier initNotifier() {
      * @return fluent builder.
      */
     public SendNotification setApplication(Application application) {
-        this.application = application;
+        this.application = checkNotNull(application);
         return this;
     }
 

send-notification/src/test/groovy/fr/jcgay/notification/SendNotificationSpec.groovy

@@ -120,4 +120,24 @@ class SendNotificationSpec extends Specification {
         then:
         PushbulletNotifier.isInstance(result)
     }
+
+    def "should get a default Application when none is set"() {
+        when:
+        def result = sendNotification
+            .setChosenNotifier('systemtray')
+            .chooseNotifier()
+
+        then:
+        result.application.name == 'Send Notification (Default)'
+        result.application.id == 'application/x-vnd-jcgay.send-notification-default'
+        result.application.icon.id == 'send-notification'
+    }
+
+    def 'should fail when trying to set a null application'() {
+        when:
+        sendNotification.setApplication(null).chooseNotifier()
+
+        then:
+        thrown(NullPointerException)
+    }
 }