title: Can't send in a second parameter to the mutation in Vue store
body: <p>I have a nice mutation JS file like this.</p>
  
  <pre><code>export default {
    UPDATE_DATA: (state, data, meta) =&gt; {
      state.dataTable = data;
  
      if (meta === undefined)
        return;
  
      state.activeDataRow = meta;
    }, ...
  }
  </code></pre>
  
  <p>It's being called by to different actions in the following ways.</p>
  
  <pre><code>context.commit("UPDATE_DATA", Map.table(payload.type, data));
  context.commit("UPDATE_DATA", Map.table(payload.type, data), meta);
  </code></pre>
  
  <p>I've checked the meta being sent in the action and it's definitely not <em>undefined</em>. However, when I check the meta in the mutation, it is! Why? How do I kill this problem?</p>