Changing type of variables without removing them

[malhar1]

First of all thank you for this excellent library..
I'm not sure if this is a bug or intended behavior..

expressionContext.Variables["salary"] = "70000";
//do some business logic and determine the 'salary' is supposed to be numeric
expressionContext.Variables["salary"] = 70000;
//evaluate expression for "salary * 1.1" ==> this causes exception

Fix/workaround:
expressionContext.Variables["salary"] = "70000";
//do some business logic and determine the 'salary' is supposed to be numeric
expressionContext.Variables.Remove("salary");
expressionContext.Variables["salary"] = 70000;
//evaluate expression for "salary * 1.1" ==> this causes exception