Implementing NA() in this formula

Hey there, this is a formula for graph data and the last point on my graph goes to zero. How do i implement na() into this formula and only show actual data on my graph?

=IF($D206>DATE('Date Key'!$B$9,'Date Key'!$B$8,1), NA(), (INDEX('Income Q'!$1:$1048576,MATCH('Graph Data Income'!$D206,'Income Q'!$A:$A,0),MATCH('Graph Data Income'!AU$205,'Income Q'!$4:$4,0))))

Thanks,

=IF($D206>DATE('Date Key'!$B$9,'Date Key'!$B$8,1), "", INDEX('Income Q'!$1:$1048576,MATCH('Graph Data Income'!$D206,'Income Q'!$A:$A,0),MATCH('Graph Data Income'!AU$205,'Income Q'!$4:$4,0)))

If the logic test is true, it will leave a blank. Blank values are left blank on a graph, whereas a NA will default to zero.