n class="fu"><a href="https://rdrr.io/r/base/NULL.html">is.null</a></span><span class="op">(</span><span class="va">input</span><span class="op">$</span><span class="va">plot_hover</span><span class="op">)</span><span class="op">)</span> <span class="op">{</span>
      <span class="va">hover</span> <span class="op">&lt;-</span> <span class="va">input</span><span class="op">$</span><span class="va">plot_hover</span>
      <span class="va">x_coord</span> <span class="op">&lt;-</span> <span class="fu"><a href=