CSHARP.NULL.RET.NONNULL : Method Should Not Return null (C#)

Summary

A method returns null but is normally assumed to return a non-null value.

If the null value gets dereferenced, C# runs into a NullReferenceException. For this reason, programmers must ensure that the content of expressions dereferenced in their programs is never null. Solving this problem is in general hard. This checker provides a coverage of the most frequent scenarios when null might end up being dereferenced. For a sound alternative to this checker, that covers all possible situations, see the Nullness checker. However, BasicNullness is much faster than Nullness and issues a more restricted set of false alarms, hence it is often the best solution for a rapid identification of the most frequent null-pointer errors in a program.

Strict and Non-Strict Checking

When CSHARP_ANALYSIS_STRICT_MODE=No, warnings of this class will not be issued if there are indications that the possibility of a NullReferenceException has been recognized and accounted for. For example, warnings will not be issued for code inside a try-catch block that explicitly catches NullReferenceException, or for a JUnit test that is annotated as expecting this exception.

When CSHARP_ANALYSIS_STRICT_MODE=Yes, warnings will be issued even in these cases.

Properties

WARNING_FILTER += discard class="Method Should Not Return null (C#)"

Example

public class ConventionExample 
{

    public static void Main(string[] args) 
    {
        
        MyClass cs = new MyClass();
        String s = cs.ToString();
    }
    
    public static class MyClass 
    {
        
        public override string ToString()
        {
            return null;  // Method Should Not Return null (C#) warning issued here
        }
    }
}

Resolution

Check if the warning corresponds to a situation where null might actually be dereferenced at runtime. If that is the case, add a nullness check for the value being dereferenced, or change the logic of the code. Sometimes, a warning of this checker corresponds to a spurious nullness check, that can be removed.

Relevant Configuration File Parameters

The following configuration file parameters affect checks for this warning class.

• CSHARP_ANALYSIS_STRICT_MODE
• REPORT_SIMILAR_WARNINGS
• WARNING_FILTER