CSHARP.NULL.RET.ARRAY : Return null Array (C#)

Summary

A method returns null instead of an empty array.

Methods with array return type should never return null, since these returned values are often used to call other methods or automatically unboxed into the primitive type. This could lead to unexpected NullPointerException.

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="Return null Array (C#)"

Example

using System;

public class TestReturnNull 
{

        public int[] returnNullForArray(int size)
        {
            if (DateTime.UtcNow.Millisecond % 2 == 0)
                return null;      // Return null Array (C#) warning issued here 
            else
                return new int[size];
        }

}

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