if function does not handle empty string as a false condition

[thetreatment]

This is perhaps a convenience rather than true bug, nonetheless it proves inconvenient.

In the case where the conditional part of an "if" function (function.Expression[0]) returns an empty string, it is not evaluated as false, it simply throws a System.FormatException from Convert.ToBoolean(object, IFormatProvider).

In fact, because of the chosen ToBoolean method used (with a format provider), many of the common true/false values cannot be used, e.g 0/1 (https://learn.microsoft.com/en-us/dotnet/api/system.convert.toboolean?view=net-8.0)

Since throwing and handling Exceptions can be processing expensive when using the Ncalc library over large data sets, it would be better to either handle a variety of values via the ToBoolean overload without a format provider, or by using Boolean.TryParse to cleanly handle cases of failed conversion and null/empty values.

[gumbarros]

I think you will need to handle empty values at OnEvaluateParameter, because an empty string is not really a false value.