Hi David,
I guess, that the same trick works:
DateListPlot[{FinancialData["GE", "Jan. 1, 2000"], FinancialData["AA", "Jan. 1, 2000"], {{{},}}}, PlotLegends -> Automatic]
The full version would be something like:
DateListPlot[{FinancialData["GE", "Jan. 1, 2000"], FinancialData["AA", "Jan. 1, 2000"], {}} /. {} -> {{{},}}, PlotLegends -> Automatic]
which gives
The main idea is that DateListPlot requires data in a different format from ListPlot. Roughly speaking a valid "empty set" for ListPlot, if the other lists are of the form {x,y}, is
{\[EmptySet]}
whereas DateListPlot requires a different "empty set". I suppose that there is a much nicer argument/way of solving this though.
Cheers,
Marco
