title: Remove legend labels using label = FALSE in guide_legend, or labels = NULL in discrete_scale
body: <p>As a part of a more complex plot with several legends, one of the legends has only one entry. I want to remove the label from this particular legend and keep only the (edited) title.</p>
  
  <pre><code>df &lt;- data.frame(x = 1, y = 1)
  
  p &lt;- ggplot(df, aes(x = x, y = y, color = factor(x))) + 
         geom_point()
  p
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/toH2F.png" alt="enter image description here"></p>
  
  <p>Because I do some other manipulations of the legends using <code>guides(foo = guide_legend(override.aes</code>, I was hoping to remove the labels in the same <code>guide_legend</code> call using the <code>label</code> argument.</p>
  
  <p>From <code>?guide.legend</code>:<br>
  "<code>label</code>: [...] If <code>FALSE</code> then the labels are invisible."</p>
  
  <p>Thus, I tried:</p>
  
  <pre><code>p + guides(color = guide_legend(title = "other",
                                  label = FALSE))
  </code></pre>
  
  <p>But this gives an error:</p>
  
  <pre><code># Error in (function (name)  : grob 'NULL' not found
  </code></pre>
  
  <p>I then had a look at <code>discrete_scale</code>, which has a <code>labels</code> argument (now with an "s"). From <code>?discrete_scale</code>:<br>
  "<code>labels</code>: <code>NULL</code> for no labels."</p>
  
  <p>Thus, I tried:</p>
  
  <pre><code>p + scale_color_discrete(name = "other",
                           labels = NULL)
  </code></pre>
  
  <p>...which generates an error:</p>
  
  <pre><code># Error in data.frame(values = scale_map(scale, breaks), labels = I(scale_labels(scale)),  : 
  #                      arguments imply differing number of rows: 1, 0
  </code></pre>
  
  <p>My current workaround is:</p>
  
  <pre><code>p + scale_color_discrete(name = "other",
                           labels = "")
  </code></pre>
  
  <p>However, as described above, I would prefer to remove the labels using <code>guide_legend</code> call.</p>
  
  <p>So my main question is:<br>
  How can I make <code>label = FALSE</code> in <code>guide_legend</code> work?   </p>
  
  <p>If the answer is "<em>it's just doesn't work</em>", how is the "<code>labels</code>: <code>NULL</code> for no labels." supposed to be used in <code>scale_foo_bar</code>?    </p>