title: How do I put legend for Na in sf_geom ggplot?
body: <p>I'm trying to make a map with information of São Paulo. To do this I'm using geobr and ggplot2. But my dataset have lot of missing data (NA), and a want put legend box to NA values. My code to generate a graph is:</p>
  <pre class="lang-r prettyprint-override"><code>ggplot(data= data, aes(geometry=geom)) +
    geom_sf(aes( fill=ite) ) +
    scale_fill_gradient(low=&quot;white&quot;, high=&quot;green&quot;,
                        na.value = &quot;red&quot;, 
                        ) +
    scale_colour_manual(values=NA)
  </code></pre>
  <p><a href="https://i.stack.imgur.com/uaU1q.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/uaU1q.png" alt="enter image description here" /></a></p>
  <p>Using geom_sf I couldn't put the legend box to NA values. The complete code is <a href="https://github.com/mj-ribeiro/College-works/blob/master/monitoring_macro/esg_map.R" rel="nofollow noreferrer">here</a>. I apreciate any help.</p>