Return empty DF when no data in get_patrol_evnts (#321)

ecoscope/io/earthranger.py

@@ -744,8 +744,10 @@ def get_patrol_events(
                         event["patrol_segment_id"] = segment.get("id")
                         events.append(event)
         events_df = pd.DataFrame(events)
-        events_df = clean_time_cols(events_df)
+        if events_df.empty:
+            return events_df
 
+        events_df = clean_time_cols(events_df)
         events_df["geometry"] = events_df["geojson"].apply(lambda x: shape(x.get("geometry")))
         events_df["time"] = events_df["geojson"].apply(
             lambda x: datetime.datetime.strptime(x.get("properties").get("datetime"), "%Y-%m-%dT%H:%M:%S%z")

tests/test_earthranger_io.py

@@ -1,5 +1,6 @@
 import datetime
 import uuid
+from unittest.mock import patch
 
 import geopandas as gpd
 import pandas as pd
@@ -154,6 +155,17 @@ def test_get_patrol_events(er_io):
     assert "time" in events
 
 
+@patch("ecoscope.io.EarthRangerIO.get_patrols")
+def test_get_patrol_events_empty(patrols_mock, er_io):
+    patrols_mock.return_value = pd.DataFrame()
+
+    events = er_io.get_patrol_events(
+        since=pd.Timestamp("2017-01-01").isoformat(),
+        until=pd.Timestamp("2017-04-01").isoformat(),
+    )
+    assert events.empty
+
+
 def test_post_observations(er_io):
     observations = gpd.GeoDataFrame.from_dict(
         [