implement empty UserInformation proper support

[jersson]

        [Fact]
        public void ValidateEmptyUserInformation()
        {
            //Given
            var userInformation = new UserInformation {
                Login = "",
                FullName = "",
                Company = "",
                Blog = "",
                Twitter = "",
                GitHubPage = "",
                PublicRepos = "",
                CreationDate = "",
                LastUpdate = "",
            };

            //When
            var result = userInformation.ToString();

            //Then
            Assert.Empty(result);
        }