error and warning messages in R console and blank downloaded plot in shiny app

Question

i am fairly new to shiny. i am trying to build ui that has drop downs (and plots/data display) that are conditional on an initial selection field. i have made a simplified example using the USArrests data set...

https://gist.github.com/guyabel/4059ae889dea4b8ca0ca

or

shiny::runGist('4059ae889dea4b8ca0ca')

i have a couple of things that i can not figure out.

1. i get error messages in the R console relating to the default plot (and subsequent plots).

   Warning in min(x) : no non-missing arguments to min; returning Inf

2. i get error messages in the R console relating to the data...

   Warning in matrix(align.tmp[(2 - pos):(ncol(x) + 1)], nrow = nrow(x), ncol = ncol(x) + : data length exceeds size of matrix

3. the download plot button returns a blank plot

4. when i select all from the first drop down i get no plot. (i guess this is related to 1)?)

any ideas how to solve any of these (i think they might all be related)?