title: Vuex commit not working without payload parameter
body: <p>I am trying to commit my global action. To access it I have to use <code>rootState</code>, so I have to add the root option parameter while commiting. It works if I pass <code>null</code> as second parameter, which is <strong>payload</strong>, but it doesn't work if I leave it empty.</p>
  
  <p>Working version:</p>
  
  <pre><code>context.commit('shared/clearError', null, { root: true })
  </code></pre>
  
  <p>Not working:</p>
  
  <pre><code>context.commit('shared/clearError, { root: true })
  </code></pre>
  
  <p>So the question is why it don't work without second parameter if it is optional as mentioned in their <a href="https://vuex.vuejs.org/api/#commit" rel="nofollow noreferrer">documentation</a>?</p>