@Test
public void artifactWithExtensionEmptyIsNotValid(){

    final Artifact artifact = DataModelFactory.createArtifact("groupId", "artifactId", "version", "classifier" , null , "");
    WebApplicationException exception = null;
    try{
        DataValidator.validatePostArtifact(artifact);
    }
    catch (WebApplicationException e){
        exception = e;
    }
    assertNotNull(exception);
}