#N/A plotted as 0 on line chart

From all I've seen, #N/A should be the value to use if you do not want blanks
to show on your line chart.

I have a table showing load times for two different databases over 30 days.

Sheet 1 shows the chart.
Sheet 2 contains VLOOKUP functions to pull the last 30 days worth of data
from Sheet 3 (which has all the data starting early December)

If I have blanks on sheet 3, my VLOOKUP functions (Looking like this:
"=IF(ISERR(VLOOKUP(I6,Driver!A:J,4,FALSE)),NA(),VL OOKUP(I6,Driver!A:J,4,FALSE))" ) correctly return "#N/A" to the cell.

When the line chart hits this particular "#N/A", it gets charted as 0. I
have the same spreadsheet, with much more manual process, which drops "#N/A"
in these blanks using a simpler IF (=IF(Driver!E22="",NA(),Driver!E22)), and
those instances result in a skipped value on the chart.

Anyone have any ideas how to get the VLOOKUP version running?