[Vala] Libgee problem

[Nicolas <c r n a wanadoo fr>]

Hello,

I need to use libgee with double.

The problem is, :
var map = new HashMap <double, double> ();

Return this error:
error: `double' is not a supported generic type argument, use `?' to box 
value types

Why libgee does not support double with hashmap?

Best regards,
Nicolas.