Get values of all string properties in current class instance

I'd like to implement a public getter which will get values of all string properties in current class instance and return it as concatinated string.

public class BaseViewModel
    {
        public string AllProperties => GetType().GetProperties().Aggregate(string.Empty, (current, prop) => prop.PropertyType == typeof(string) ? current + (string)prop.GetValue(this, null) : current);
    }

public class ChildViewModel : BaseViewModel
{
    public string prop1 { get; set; }
    public string prop2 { get; set; }
}

When I run this I get StackOverflowException..