Query Editor R Script Date Time Issues

So I'm trying to use the Run R Script in the Query Editor. I'd like to run statistical models using R, however, doing even the simpliest tasks seem a bit difficult.

It seems that the 'dataset' provided automatically is a data.frame, but the columns that have a datetime are converted to factors I was able to verify that doing the following:

# 'dataset' holds the input data for this script
output <- dataset
output$discovery_date_utc_type <- class(output$discovery_date_utc)

The result is factor, so I did the following to get around that... 

output <- as.data.frame(dataset, stringsAsFactors = FALSE)

Then I was able to manipulate the column back into a datetime column doing the following:

# I previously loaded the lubridate package as I was still having issues with standard R date time data types??? It would work in RStudio, but not in PowerBI 
#library(lubridate)
output$discovery_date_utc_new <- ymd_hms(result$discovery_date_utc)

This worked!!!! Yeah The output data frame has a new column and it is a date time column. 

Now here is my issue... 
I then wanted to get the maximum date and put that into a variable end_date... but I'm getting an error.

end_date <- max(output$discovery_date_utc_new)

Resulting Error (this works fine in RStudio):

DataSource.Error: ADO.NET: R script error.
Warning message:
In scan(file = file, what = what, sep = sep, quote = quote, dec = dec,  :
  embedded nul(s) found in input
Loading required package: methods

Attaching package: 'lubridate'

The following object is masked from 'package:base':

    date

Error in lapply(list(...), .num_to_date) : object 'result' not found
Calls: ymd_hms -> .parse_xxx_hms -> unlist -> lapply
Execution halted

Details:
    DataSourceKind=R
    DataSourcePath=R
    Message=R script error.
Warning message:
In scan(file = file, what = what, sep = sep, quote = quote, dec = dec,  :
  embedded nul(s) found in input
Loading required package: methods

Attaching package: 'lubridate'

The following object is masked from 'package:base':

    date

Error in lapply(list(...), .num_to_date) : object 'result' not found
Calls: ymd_hms -> .parse_xxx_hms -> unlist -> lapply
Execution halted

    ErrorCode=-2147467259
    ExceptionType=Microsoft.PowerBI.Radio.RScriptRuntimeException