title: Colormap issue in folium map
body: <p>I am looking to create a heatmap of the USA based on data of COVID 19 cases. For that, I am using folium and geopandas. Here is the <a href="https://www.mediafire.com/file/uzex42odlg9cxak/data.xlsx/file" rel="nofollow noreferrer">link for the data</a></p>
  
  <p>and the code I used is given below.</p>
  
  <pre><code>colormap = cm.linear.YlGnBu_09.to_step(data=merged_data_cases['cases'], 
             method='quant', quantiles=[0,0.1,0.75,0.9,0.98,1]
  
  usa_map = folium.Map(location=[48, -102], zoom_start=3, tiles=None)
  folium.TileLayer('CartoDB positron',name="Light Map",control=False).add_to(usa_map)
  colormap.caption = 'Confirmed Cases'
  
  
  style_function = lambda x: {"weight":0.5, 
                          'color':'black',
                          'fillColor':colormap(x['properties']['cases']), 
                          'fillOpacity':0.75}
  highlight_function = lambda x: {'fillColor': '#000000', 
                             'color':'#000000', 
                              'fillOpacity': 0.50, 
                              'weight': 0.1}
  interactive = folium.features.GeoJson(
                  merged_data_cases,
                  style_function=style_function, 
                  control=False,
                  highlight_function=highlight_function, 
          tooltip=folium.features.GeoJsonTooltip(
                   fields=['Name','cases'],
                   aliases=['State: ','Confirmed Cases: '],
                   style=("background-color: white; color: #333333; font-family: arial; font-size: 12px; padding: 10px;"),
      sticky = True
     )
  )
     colormap.add_to(usa_map)
     usa_map.add_child(interactive)
     usa_map
  </code></pre>
  
  <p>While I run the code, I get the following error. </p>
  
  <pre><code>AssertionError: The field Name is not available in the data. Choose from: ('NAME', 'STATE', 'cases').
  </code></pre>
  
  <p>I have gone through so many articles, blogs and documentation but still couldn't figure out my error. Can anybody point out what I am doing wrong here? I believe the error is due to style_function parameters.  </p>