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How to Resolve Warning "CS0458: The result of the expression is always 'null' of type 'int?' (or other nullable type)" in C#

The Compiler Warning CS0458 is a Code Quality and Logic warning. The message reads: "The result of the expression is always 'null' of type 'type name'".

This warning appears when the C# compiler analyzes an expression and determines that, due to the rules of Nullable types or constant propagation, the result will always be null at runtime. The code technically compiles, but it serves no purpose because the outcome is fixed before the program even runs. This usually happens with mathematical operations involving null literals or redundant null-coalescing operations.

This guide explains the behavior of "lifted operators" and how to fix pointless logic.

Understanding Null Propagation​

In C#, operations on Nullable Value Types (int?, bool?, double?) follow a specific rule: If one operand is null, the result is null.

  • 5 + null = null
  • true & null = null
  • 10 * (int?)null = null

If you hardcode null (or a constant that casts to null) into one side of these equations, the compiler sees that the math is pointless because the result can never be anything other than null.

Scenario 1: Arithmetic with Null Literals​

This is the most common cause. You might be testing logic or have a typo where you explicitly cast null to a nullable type and use it in math.

Example of warning​

public class Calculator
{
    public void Calculate()
    {
        int? offset = 10;

        // ⛔️ Warning CS0458: The result of the expression is always 'null' of type 'int?'
        // Adding 'null' to '10' essentially deletes the '10'.
        int? result = offset + (int?)null;
        
        System.Console.WriteLine(result.HasValue); // Always False
    }
}

Solution: Remove the Null Operation​

If you intended to add "nothing," simply use the variable as is. If you intended to initialize a variable to null, assign it directly.

public class Calculator
{
    public void Calculate()
    {
        int? offset = 10;

        // ✅ Correct: Just use the variable if adding 0/null was the intent
        int? result = offset;
        
        // OR, if you intended to reset it:
        // int? result = null;
    }
}

Scenario 2: Redundant Null Coalescing​

The null-coalescing operator (??) returns the left-hand operand if it isn't null; otherwise, it returns the right-hand operand.

If the right-hand operand is explicitly null, the operation does nothing useful.

  • If Left is not null -> Returns Left.
  • If Left is null -> Returns null. In both cases, the result is identical to just Left (conceptually), or explicitly null if the types force it.

Example of warning​

public class Data
{
    public void Process(int? input)
    {
        // ⛔️ Warning CS0458: The result is always null? 
        // Actually, specifically if you try to coalesce two null constants:
        int? val = (int?)null ?? null;
    }
}

Solution: Assign Explicitly​

Don't use logic to arrive at a constant null.

public class Data
{
    public void Process(int? input)
    {
        // ✅ Correct: Just assign null
        int? val = null;
    }
}

Conclusion​

CS0458 is the compiler telling you that your code is doing extra work for zero result.

  1. Check Math: Are you adding, subtracting, or multiplying by (int?)null? Remove that part of the equation.
  2. Check Logic: Are you comparing or coalescing against null in a way that guarantees a null output? Simplify the expression to a direct assignment.

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