Static parameters don't get applied

Question

I recently tried nCalc for parsing formula from strings. But when I tried static parameters I always ended with null as a result. Here is the example I tried:

Expression e = new Expression("[bProd] + [bUp]");

e.Parameters["bProd"] = 50;
e.Parameters["bUp"] = 60;

var res = e.Evaluate();

Where res is always null. The nCalc Doc about static didn't helped me. Can anyone point me to the problem? I am using the latest version of nCalc included using nuget.