added reproducible example to insert null records for safety echart

[cyyllam]

Added a stand alone reproducible example of null records being added to the main table (data_clean object) to produce the final line chart.

• Run the R script before incorporating the the section that adds null data to make sure chart is good
• Lines 14 to 43 can be copied and pasted into your choice of .Rmd, whatever your preference is for this process to happen.