Nullable variables (int?) cause error on evaluation when value is null

[maharateeq]

When setting a nullable variable (int?) with a null value, DynamicExpresso throws an evaluation error instead of handling the expression correctly.

var interpreter = new DynamicExpresso.Interpreter();

int? MyVar = null;

interpreter.SetVariable("MyValue", MyVar, typeof(int?));

var result = interpreter.Eval("(MyValue ?? 0) == 2");

Event These Evaluation Fails :

((int?)2 ?? 0) == 2      // Should be true, but throws
((int?)null ?? 0) == 2   // Should be false, but throws

Expected behaviour : The expression should evaluate without error and return false.

Actual behavior: It throws an InvalidOperationException.

Expected issue : DynamicExpresso treats (nullable ?? value) as returning object instead of the underlying type (int in this case).

Can someone please help me identify is it a bug/my wrong of of using and some other way possible to handle the scenario.

I am using Version : 2.19.2 (Latest as of now)

[metoule]

It's indeed a bug. It's due to the way we convert the null-coalescing operator: we generate the following pseudo code:

const object nullConst = null;
int? MyVar = null;
return MyVar == nullConst ? 0 : MyVar;

but int? can't be compared to an object, which is why it fails. We should have a dedicated code path for nullables.

The issue comes from this line:

DynamicExpresso/src/DynamicExpresso.Core/Parsing/Parser.cs

Line 252 in b0aeeb3

expr = GenerateConditional(GenerateEqual(expr, ParserConstants.NullLiteralExpression), exprRight, expr, errorPos);

[maharateeq]

Just as a side note for other Types.

Same result was in case of decimal? as it was int?

[metoule]

Yes, the underlying type doesn't matter, all nullables are now handled.

[maharateeq]

by the way this behaviour repeat in other operators too , including > , < , => , =< etc,. :(

[metoule]

Ah.. Thanks for checking, I'll see how to handle all binary operators.