UnmarshalExtJSON fail:

~~~
data := `[ "201810", "201811" ]`

arr := bson.NewArray()
err := bson.UnmarshalExtJSON([]byte(data), true, &arr)
if err != nil

t.Log(arr)
~~~

 
output:
~~~
Cannot read unknown BSON type invalid
~~~

but if data = 'data := `[ "201810" ]` works well