Line chart different line styles for different lines

[m23]

Hi All,
I hope someone can help me with this.

I have data as follows

X            Y        Series1      Series2
1999       1          line1           null
1999       3          null             line2
2000       4          line1           null
2000       5          null             line2

I am putting this on a line chart in report studio. X goes in the X axis Y goes in the Y axis and I have put series 1 as the first series and series 2 as the second series. What I would like is for line 1 to be a solid line with points plotted and line 2 to be a dotted line with no points plotted. So I have setup the separate line styles for the first and second series. It almost works but it also plots the null values. Does anyone know of a way to do this?  I could also format the data

X            Y        Series1     
1999       1          line1         
1999       3          line2
2000       4          line1       
2000       5          line2

If that makes it easier.

I suspect it's not possible but hope someone can prove me wrong.