Null check can be simplified (IDE0029, IDE0030, and IDE0270)

This article describes three related rules, IDE0029, IDE0030, and IDE0270.

Overview

Rules IDE0029 and IDE0030 concern the use of null-coalescing expressions, for example, x ?? y, versus ternary conditional expressions with null checks, for example, x != null ? x : y. The rules differ with respect to the nullability of the expressions:

• IDE0029: Used when non-nullable expressions are involved. For example, this rule could recommend x ?? y instead of x != null ? x : y when x and y are non-nullable reference types.
• IDE0030: Used when nullable expressions are involved. For example, this rule could recommend x ?? y instead of x != null ? x : y when x and y are nullable value types or nullable reference types.

Rule IDE0270 flags the use of a null check (== null or is null) instead of the null-coalescing operator (??).

Options

Options specify the behavior that you want the rule to enforce. For information about configuring options, see Option format.

dotnet_style_coalesce_expression

Examples

IDE0029 and IDE0030

// Code with violation.
var v = x != null ? x : y; // or
var v = x == null ? y : x;

// Fixed code.
var v = x ?? y;

' Code with violation.
Dim v = If(x Is Nothing, y, x) ' or
Dim v = If(x IsNot Nothing, x, y)

' Fixed code.
Dim v = If(x, y)

IDE0270

// Code with violation.
class C
{
    void M()
    {
        var item = FindItem() as C;
        if (item == null)
            throw new System.InvalidOperationException();
    }

    object? FindItem() => null;
}

// Fixed code (dotnet_style_coalesce_expression = true).
class C
{
    void M()
    {
        var item = FindItem() as C ?? throw new System.InvalidOperationException();
    }

    object? FindItem() => null;
}

' Code with violation.
Public Class C
    Sub M()
        Dim item = TryCast(FindItem(), C)
        If item Is Nothing Then
            item = New C()
        End If
    End Sub

    Function FindItem() As Object
        Return Nothing
    End Function
End Class

' Fixed code (dotnet_style_coalesce_expression = true).
Public Class C
    Sub M()
        Dim item = If(TryCast(FindItem(), C), New C())
    End Sub

    Function FindItem() As Object
        Return Nothing
    End Function
End Class

Suppress a warning

If you want to suppress only a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

#pragma warning disable IDE0029 // Or IDE0030 or IDE0270
// The code that's violating the rule is on this line.
#pragma warning restore IDE0029 // Or IDE0030 or IDE0270

To disable the rule for a file, folder, or project, set its severity to none in the configuration file.

[*.{cs,vb}]
dotnet_diagnostic.IDE0029.severity = none
dotnet_diagnostic.IDE0030.severity = none
dotnet_diagnostic.IDE0270.severity = none

To disable all of the code-style rules, set the severity for the category Style to none in the configuration file.

[*.{cs,vb}]
dotnet_analyzer_diagnostic.category-Style.severity = none

For more information, see How to suppress code analysis warnings.

See also

• Code style language rules
• Code style rules reference