I used this code to log the top 3 dollar volume, the output was : 

['AOL', 'INTC', 'YHOO']

However, according to the research environment, there is no output for AOL.

class CoarseFundamentalTopAlgorithm(QCAlgorithm):

def Initialize(self):

self.SetStartDate(1999,1,11)
self.SetEndDate(1999,1,12)
self.SetCash(10000)

self.UniverseSettings.Resolution = Resolution.Daily

self.AddUniverse(self.Universe.DollarVolume.Top(3))

self.__numberOfSymbols = 3

def OnData(self, data):

x = []
for key in data.Keys:
x.append(str(key.Value))
x.sort()

self.Log(x)