Is your feature request related to a problem? Please describe.
given an expression like: @2020-01-01 - 365 days previously it was possible to:

var fpCompiler = new FhirPathCompiler(
        new SymbolTable()
            .AddStandardFP()
            .AddFhirExtensions()
    );
var exp = fpCompiler.Compile("@2020-01-01 - 365 days");
var res = exp(null!, new EvaluationContext()).FirstOrDefault();

but with newer versions, you get an exception that the node parameter is null. Not sure where exactly the change was made.

Describe the solution you'd like
I want to call the compiled expression with null

or

provider a different method or Compile overload that will return a different delegate that doesn't need a node.

Describe alternatives you've considered
supplying something like exp(new Patient().ToPocoNode(), new EvaluationContext()) works, but not ideal.

Additional context
n/a