/// <summary>
 /// Registers a Custom Expression Factory
 /// </summary>
 /// <param name="factory">A Custom Expression Factory</param>
 public static void AddCustomFactory(ISparqlCustomExpressionFactory factory)
 {
     // Only register the factory if it is not already registered
     if (!CustomFactories.Any(f => f.GetType().Equals(factory.GetType())))
     {
         CustomFactories.Add(factory);
     }
 }
 /// <summary>
 /// Registers a Custom Expression Factory
 /// </summary>
 /// <param name="factory">A Custom Expression Factory</param>
 public static void AddCustomFactory(ISparqlCustomExpressionFactory factory)
 {
     //Only register the factory if it is not already registered
     if (!_customFactories.Any(f => f.GetType().Equals(factory.GetType())))
     {
         _customFactories.Add(factory);
     }
 }