If the map does not display and instead it displays this error, most likely it’s something related with your markers coordinates.
Cannot read property '0' of null
This is how the error looks like:
This is more common when using the USA map with the AlbersUSA projection. Some operations fail when the coordinates added for a marker sit outside the visible area of the chosen map.
For example, if you’re using the US map but add coordinates for a location in Europe, you might come across this issue.
Review your marker coordinates and if this starts happening after a particular marker was added, make sure the coordinates are correct and inside the area of the selected map.