Typescript coverage seems incorrect with tsc

It seems that the coverage is not correct with the function that I'd like to test :

public isSelfTweet = function(tweet: Tweet, twitterScreenName: string) {
    if(null == tweet || null == tweet.user || null == tweet.user.screen_name) {
        return false;
    }
    if(tweet.user.screen_name.toLowerCase() === twitterScreenName) {
        return true;
    }
    return false;
}

I write three tests and I have a 100% coverage :

• tweet = null, twitterScreenName = "toto"
• tweet with screen_name = "toto", twitterScreenName = "toto"
• tweet with screen_name = "toto", twitterScreenName = "tutu"

Here is the coverage which seems incorrect for me. I never have tested tweet not null, but tweet.user null for instance

In my package json :

"nyc": "^11.2.1",