/// <summary>
 /// Extension method to get fhir generic type extension
 /// </summary>
 /// <param name="resource"></param>
 public static IEnumerable <ElementDefinition> GetGenericTypes(this IExtendable resource)
 {
     foreach (Extension ext in resource.GetExtensions(GenericExtensionUri))
     {
         yield return((ElementDefinition)ext.Value);
     }
 }