If you have data with different time ranges eg. stock1 from 01/01/.2009 till 31/12/2010 and stock2 with data from 01/01/2010 till 31/12/2011 open the graph for stock1 and the range in the x-axis is painted till 31/12/2011. The vertical line descriptors appear at the end of the data range 2011. I don't think that this is necessary. The range of the x-axis should only be painted for data (or graphs) that is currently shown (e. g. if we compare two stocks in one chart).
Now, highlight the range where we don't have data for stock1 (01/01/2011 till 31/12/2011). Then hit the ZoomIn button. You'll get an error message. That's ok, but the ZoomIn button remains enabled. If you hit it again you'll get a NullPointerException. So, we should disable the ZoomIn button if the error message is shown.
I'll try to fix this.