User: add more constraints

Signed-off-by: Pekka Helenius <fincer89@hotmail.com>

bookstore/src/main/java/com/fjordtek/bookstore/model/auth/User.java

@@ -83,6 +83,7 @@ public class User {
 			nullable = false,
 			columnDefinition = "NVARCHAR(" + strMax + ")"
 			)
+	@NotBlank
 	private String email;
 
 	@OneToMany(