title: ValueError: Location values cannot contain NaNs, got: [nan, nan]
body: <pre><code>import folium
  import pandas
  
  data= pandas.read_csv("maps.txt")
  
  lat = list(data["latitude"])
  lon = list(data["longitude"])
  
  map= folium.Map(location=[31.5204, 74.3587], zoom_start=6, tiles="Mapbox Bright")
  
  fg = folium.FeatureGroup(name="My Map")
  
  for lt, ln in zip(lat, lon):
      c1 = fg.add_child(folium.Marker(location=[lt, ln], popup="Hi i am a Country",icon=folium.Icon(color='green')))
  
  child = fg.add_child(folium.Marker(location=[31.5204, 74.5387], popup="Welcome to Lahore", icon= folium.Icon(color='green')))
  
  map.add_child(fg)
  </code></pre>
  
  <pre>
  Traceback (most recent call last):
    File "C:\Users\Ryan\AppData\Local\Programs\Python\Python36-32\check2.py", line 14, in 
      c1 = fg.add_child(folium.Marker(location=[lt, ln], popup="Hi i am a Country",icon=folium.Icon(color='green')))
    File "C:\Users\Ryan\AppData\Local\Programs\Python\Python36-32\lib\site-packages\folium\map.py", line 647, in __init__
      self.location = _validate_coordinates(location)
    File "C:\Users\Ryan\AppData\Local\Programs\Python\Python36-32\lib\site-packages\folium\utilities.py", line 48, in _validate_coordinates
      'got:\n{!r}'.format(coordinates))
  ValueError: Location values cannot contain NaNs, got:
  [nan, nan]
  </pre>
  
  <pre><code>map.save("Lahore.html")
  </code></pre>
  
  <p>Actually i was making markerss of the map using txt file (commas separated) it opened successfully but i wanted all those adresses of countries to become markers and when i tried it just gave this error.</p>