Code inspection: Declaration nullability inferred (parameter is inferred to be nullable)

This inspection reports a parameter that control-flow analysis infers may legitimately be null. This usually happens when the method checks the parameter for null, uses conditional access, or otherwise handles the null case explicitly. Adding [CanBeNull] documents that callers are allowed to pass null.

Example

In this example, the builder parameter is used with conditional access (?.). The quick-fix suggests adding the [CanBeNull] attribute.

                using System.Text;

                public class Formatter
                {
                    public void WriteLine(StringBuilder builder)
                    {
                        builder?.AppendLine();
                    }
                }
            

                using System.Text;
                using JetBrains.Annotations;

                public class Formatter
                {
                    public void WriteLine([CanBeNull] StringBuilder builder)
                    {
                        builder?.AppendLine();
                    }
                }
            

Quick-fix

Annotate the parameter with the inferred nullability attribute, usually [CanBeNull]. For container-like parameters, the quick-fix can use [ItemCanBeNull] instead.

28 March 2026