Running examples in 'eechidna-Ex.R' failed
The error most likely occurred in:

> base::assign(".ptime", proc.time(), pos = "CheckExEnv")
> ### Name: nat_data_download
> ### Title: Download a data frame containing electorate centroids
> ### Aliases: nat_data_download
> 
> ### ** Examples
> 
> library(eechidna)
> library(dplyr)

Attaching package: 'dplyr'

The following objects are masked from 'package:stats':

    filter, lag

The following objects are masked from 'package:base':

    intersect, setdiff, setequal, union

> library(ggmap)
Loading required package: ggplot2
Google's Terms of Service: https://cloud.google.com/maps-platform/terms/.
Please cite ggmap if you use it! See citation("ggmap") for details.
> 
> nat_data19 <- nat_data_download(2019)
trying URL 'https://github.com/jforbes14/eechidna/raw/master/extra-data/nat_data19.rda'
Content type 'application/octet-stream' length 7727 bytes
==================================================
downloaded 7727 bytes

> 
> nat_data19 %>%
+   qmplot(long_c, lat_c, data=.)
Using zoom = 5...
Source : http://tile.stamen.com/terrain/5/26/16.png
Source : http://tile.stamen.com/terrain/5/27/16.png
Source : http://tile.stamen.com/terrain/5/28/16.png
Source : http://tile.stamen.com/terrain/5/29/16.png
Source : http://tile.stamen.com/terrain/5/26/17.png
Source : http://tile.stamen.com/terrain/5/27/17.png
Source : http://tile.stamen.com/terrain/5/28/17.png
Source : http://tile.stamen.com/terrain/5/29/17.png
Source : http://tile.stamen.com/terrain/5/26/18.png
Source : http://tile.stamen.com/terrain/5/27/18.png
Source : http://tile.stamen.com/terrain/5/28/18.png
Source : http://tile.stamen.com/terrain/5/29/18.png
Source : http://tile.stamen.com/terrain/5/26/19.png
Source : http://tile.stamen.com/terrain/5/27/19.png
Source : http://tile.stamen.com/terrain/5/28/19.png
Source : http://tile.stamen.com/terrain/5/29/19.png
Source : http://tile.stamen.com/terrain/5/26/20.png
Source : http://tile.stamen.com/terrain/5/27/20.png
Source : http://tile.stamen.com/terrain/5/28/20.png
Source : http://tile.stamen.com/terrain/5/29/20.png
Error in UseMethod("as.raster") : 
  no applicable method for 'as.raster' applied to an object of class "NULL"
Calls: %>% ... qmplot -> get_map -> get_stamenmap -> stitch -> as.raster
Execution halted