change site default to None

hydrofunctions/station.py

@@ -12,10 +12,11 @@
 class Station(object):
     """A class for organizing stream gauge data for a single site."""
 
-    def __init__(self, site="", service="dv", start_date=None, end_date=None):
+    def __init__(self, site=None, service="dv", start_date=None, end_date=None):
         self.site = site
         self.service = service
         self.start_date = start_date
         self.end_date = end_date
 
-
+    def fetch(self):
+        get_nwis(self.site, self.service, self.start_date, self.end_date)

tests/test_station.py

@@ -16,9 +16,9 @@ def test_station_is_obj(self):
         actual = station.Station()
         self.assertIsInstance(actual, station.Station)
 
-    def test_station_site_defaults_to_empty_str(self):
+    def test_station_site_defaults_to_None(self):
         actual = station.Station()
-        self.assertEqual(actual.site, "")
+        self.assertIsNone(actual.site)
 
     def test_station_site_sets(self):
         expected = "0123"