adding asv for Series Nunique() with Nan values

Author: Kenil Mehta

asv_bench/benchmarks/frame_methods.py

@@ -562,6 +562,12 @@ def setup(self):
     def time_frame_nunique(self):
         self.df.nunique()
 
+class SeriesNuniqueWithNan:
+    def setup(self):
+        self.ser = Series(100000 * (100 * [np.nan] + list(range(100)))).astype(float)
+
+    def time_series_nunique_nan(self):
+        self.ser.nunique()
 
 class Duplicated:
     def setup(self):