NSMutableArray adds NSMutableArray

I am trying to set the content of my allArticlesArray and then add an array with additional objects. Here's a snippet of my code to do it:

[self.allArticlesArray setArray:newsArray];
[self.allArticlesArray addObjectsFromArray:sportsArray];

      

        
        
        
      

    

newsArray and sportsArray are non-zero (each has five elements), but after running this code, allArticlesArray is null. I am using ARC. What am I doing wrong? Thank you!