I am not seeing any NULLs. Every day of the year has a value if I drag Electricity Used in to the table.
Under the Analysis menu do you have column totals turned on?
Sent from the iPhone of Timothy Dines.
It looks like you are having a problem with using the wrong locale and so dates are getting confused between MM/DD/YYYY order and DD/MM/YYYY order. That's not supposed to cause problems, but it looks likely to be the problem in your case since you are getting days only up to 12.
What are the language and locale settings on your machine?