Sonar issues with null check C#

Question

After enabling Sonar in my project I get the following message

myEntities is null on at least one execution path.

public static IEnumerable<KeyValuePair<MyDto,long>> PrepareClientResponses(this IEnumerable<MyServiceCnt> myEntities)
{
    if (myEntities == null || !myEntities.Any())
    {
        yield return default;
    }         
    foreach (var myEntities in myEntities)
    {
        var client = myEntities.PrepareClientResponse();
        yield return new KeyValuePair<MyDto, long>(client, myEntities.MyId.Value);
    }
}

The message is on the "myEntities" on the foreach (var myEntities in myEntities) line.

Can someone suggest me on how to solve this message. I am checking null condition but it still gives this warning.

`foreach (var myEntities in myEntities)` is wrong, you're using the very same variable! Shouldn't it be `foreach (var myEntity in myEntities)`? — Marco, Mar 14 '23 at 07:44
@Marco `foreach (var myEntities in myEntities)` even *does not compile* since `myEntities` is also a parameter in the method. — Mustafa Özçetin, Mar 15 '23 at 05:45
Its actually a copy paste mistake from myend..rectified in my code @Mustafa — coder11 b, Mar 15 '23 at 10:23

dan1st · Accepted Answer · 2023-03-15T21:29:20.060

yield return default;

yield return roughly means "give back a value and continue once the next value is requested".

So, the loop is executed even if the yield return is never reached.

For fixing this, you have multiple options.

`yield break`

Instead of the yield return in the if, you can use yield break in order to terminate the method as explained here.

public static IEnumerable<KeyValuePair<MyDto,long>> PrepareClientResponses(this IEnumerable<MyServiceCnt> myEntities)
{
    if (myEntities == null || !myEntities.Any())
    {
        yield return default;
        yield break;
    }
    foreach (var e in myEntities)
    {
        var client = e.PrepareClientResponse();
        yield return new KeyValuePair<MyDto, long>(client, e.MyId.Value);
    }
    
}

`else`

You can just put the loop in an else-block. This way, it won't be executed in case the check evaluates to true:

public static IEnumerable<KeyValuePair<MyDto,long>> PrepareClientResponses(this IEnumerable<MyServiceCnt> myEntities)
{
    if (myEntities == null || !myEntities.Any())
    {
        yield return default;
    }
    else
    {
        foreach (var e in myEntities)
        {
            var client = e.PrepareClientResponse();
            yield return new KeyValuePair<MyDto, long>(client, e.MyId.Value);
        }
    }
}

do nothing

In some cases, it might be a sensible decision to not return any element in case a preconception fails. But note that your code will behave differently if you arr doing that.

public static IEnumerable<KeyValuePair<MyDto,long>> PrepareClientResponses(this IEnumerable<MyServiceCnt> myEntities)
{
    if (myEntities != null && myEntities.Any())
    {
        foreach (var e in myEntities)
        {
            var client = e.PrepareClientResponse();
            yield return new KeyValuePair<MyDto, long>(client, e.MyId.Value);
        }
    }
}

other problem

Please see this other answer by @Marco for another problem with your code (which I also integrated in this answer).

Thanks , i have implemented the second case ie with "else " implementation and bug got resolved. Also have incorporated @Macros s point also to work. — coder11 b, Mar 14 '23 at 15:24
@dan1st here yield return default; yield break; yield break is only needed here? Should i have yield return as well as yield break — coder11 b, Mar 15 '23 at 20:10
if you use `yiels return default` before `yield break`, you woukd get the value `default` when iterating over it. If you just use `yield break;`, it will be empty. — dan1st, Mar 15 '23 at 21:28

score 2 · Answer 2 · answered Mar 14 '23 at 07:46

You have an error in your foreach loop: foreach (var myEntities in myEntities)

It is wrong because you're using the very same variable for the loop!
It should be:

foreach (var myEntity in myEntities)
{
    var client = myEntity.PrepareClientResponse();
    yield return new KeyValuePair<MyDto, long>(client, myEntity.MyId.Value);
}

Sonar issues with null check C#

2 Answers2

yield break

else

do nothing

other problem

`yield break`

`else`