Adds a test to the modify method in PeopleResourceUnitTest class

This test was unintentionally leaved out when creating the test case.

src/test/java/es/uvigo/esei/daa/rest/PeopleResourceUnitTest.java

@@ -193,6 +193,18 @@ public class PeopleResourceUnitTest {
 		assertThat(response, hasBadRequestStatus());
 	}
 
+	@Test
+	public void testModifyNullPointerException() throws Exception {
+		daoMock.modify(anyObject());
+		expectLastCall().andThrow(new NullPointerException());
+		
+		replay(daoMock);
+
+		final Response response = resource.modify(existentId(), newName(), newSurname());
+		
+		assertThat(response, hasBadRequestStatus());
+	}
+
 	@Test
 	public void testAdd() throws Exception {
 		expect(daoMock.add(newName(), newSurname()))