title: When looping over an array of objects and adding data to a variable, it always adds an null along with the data
body: <p>I have a an array of objects, and when I am looping over it add adding a value to a variable, the variable always has an nullin it. I know its a pretty basic question, but stuck on why it adds the null and don't know how to stop it.</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>(function() {
    let ds = [{
        Name: "A",
        Age: 1
      },
      {
        Name: "B",
        Age: 2
      },
      {
        Name: "C",
        Age: 3
      }
    ];
    let str = null;
  
    for (let i = 0; i &lt; ds.length; i++) {
      if (ds[i].Name) {
        str += ds[i].Name + ",";
      }
    }
    console.log(str);
  })();</code></pre>
  </div>
  </div>
  </p>
  
  <p>It shows as null, A, B, C, and what I want it to show as A,B,C</p>