title: Heatmap error "TraitError: The 'locations' trait of a Heatmap instance must be of length"
body: <p>I'm trying to run a code that registers coordinates onto a heat map using Javascript on Jupyter Notebook. My code is:</p>
  <pre><code>import gmaps
  import gmaps.datasets
  gmaps.configure(api_key=&quot;MY API KEY&quot;)
  
  data = [(-89.91161093276477, 35.241969778429194), (-89.87947624903887, 35.195319161704404), (-89.81418532101328, 35.17188216058175), (-89.75643652692003, 35.183538628834484), (-89.7496498284386, 35.14509890887518), (-89.78504762327763, 35.063349559432304), (-89.83100682136623, 35.013757847903044), (-89.85342496546569, 35.001086997562474)]
  m = gmaps.Map()
  heatmap_layer = gmaps.Heatmap(data=data)
  m.add_layer(heatmap_layer)
  m
  </code></pre>
  <p>But I keep on getting the error:</p>
  <pre><code>TraitError: The 'locations' trait of a Heatmap instance must be of length 1 &lt;= L &lt;= 9223372036854775807, but a value of [] was specified.
  </code></pre>
  <p>What does this mean and how can I fix it?</p>