AddRange throws "Cannot implicitly convert type" exception : <p>I have no idea why this is not working:</p>

<pre><code>    Dictionary&lt;string, List&lt;GameObject&gt;&gt; prefabs = new Dictionary&lt;string, List&lt;GameObject&gt;&gt;();
    List&lt;GameObject&gt; slotPrefabs = new List&lt;GameObject&gt;();

    // yadda yadda yadda

    if (prefabs.ContainsKey(slot))
    {
        prefabs[slot] = prefabs[slot].AddRange(slotPrefabs);
    }
    else
    {
        prefabs.Add(slot, slotPrefabs);
    }
</code></pre>

<p>It's giving me:</p>

<blockquote>
  <p>Cannot implicitly convert type 'void' to 'System.Collections.Generic.List'</p>
</blockquote>

<p>I just want to add to the existing list of the dictionary key if it already exists.</p>
