title: How to set the different legend icon for different series in same chart
body: <p><a href="https://i.stack.imgur.com/AZGLn.png" rel="nofollow noreferrer">enter image description here</a></p>
  
  <p>As shown in the figure above, I need to remove the circle in the middle of the third icon, but keep the shape of the other two charts rectangular.But when I set <code>legend.icon = 'line'</code>, the shape of the other two icons changed.What should I do?</p>