Evitando ValidatorException quando CPF é vazio

Isso é trabalho do validator required
diff --git a/stella-faces/src/main/java/br/com/caelum/stella/faces/validation/StellaCPFValidator.java b/stella-faces/src/main/java/br/com/caelum/stella/faces/validation/StellaCPFValidator.java
index 44518d6..1eca492 100644
--- a/stella-faces/src/main/java/br/com/caelum/stella/faces/validation/StellaCPFValidator.java
+++ b/stella-faces/src/main/java/br/com/caelum/stella/faces/validation/StellaCPFValidator.java
@@ -57,7 +57,7 @@
     }
 
     public void validate(FacesContext facesContext, UIComponent uiComponent, Object value) throws ValidatorException {
-    	if (value == null) return;
+    	if (value == null || "".equals(value)) return; // deixa o validador required fazer seu trabalho
     	
         ResourceBundle bundle = resourceBundleFinder.getForCurrentLocale(facesContext);
         ResourceBundleMessageProducer producer = new ResourceBundleMessageProducer(bundle);
diff --git a/stella-faces/src/test/java/br/com/caelum/stella/faces/validation/StellaCPFValidatorTest.java b/stella-faces/src/test/java/br/com/caelum/stella/faces/validation/StellaCPFValidatorTest.java
index 6e315dd..2c5865a 100644
--- a/stella-faces/src/test/java/br/com/caelum/stella/faces/validation/StellaCPFValidatorTest.java
+++ b/stella-faces/src/test/java/br/com/caelum/stella/faces/validation/StellaCPFValidatorTest.java
@@ -105,4 +105,18 @@
         	fail("shouldn't throw exception for null cpf");
         }
     }
+
+    @Test
+    public void shouldNotThrowValidatorExceptionWhenCPFIsEmpty() {
+        final FacesContext context = mockery.mock(FacesContext.class);
+        final UIComponent component = mockery.mock(UIComponent.class);
+        facesContextMocker.mockMessageBundle(context, "messages", Locale.getDefault());
+
+        try {
+            validator.validate(context, component, "");
+            mockery.assertIsSatisfied();
+        } catch (ValidatorException e) {
+            fail("shouldn't throw exception for empty cpf");
+        }
+    }
 }