[Bug] Nullable value types aren't supported in navigation parameters

[BurkusCat]

Describe the bug You can't use GetValue<char?> without getting an exception

To Reproduce Steps to reproduce the behavior:

1. Add code such as:

   var test = parameters.GetValue<char?>("test");

2. Observe exception

   System.ArgumentException : Cannot convert parameter value to type System.Nullable`1[System.Char]
   ---- System.InvalidCastException : Null object cannot be converted to a value type.

Expected behavior The framework supports passing nullable value types.