PicarroProvider. Better manage case when Picarro data is missing.

src/dataprovider/picarroprovider.py

@@ -15,7 +15,6 @@ class PicarroProvider:
         self.root_dir = config.read("DATA_SOURCE", "picarro_root_dir") + "/"\
                         + self.picarro_id + "/"
 
-
     def get_df(self, first_datetime: datetime.datetime, last_datetime: datetime.datetime, columns: list):
         if (first_datetime.year == last_datetime.year) \
                 & (first_datetime.month == last_datetime.month) \
@@ -23,6 +22,9 @@ class PicarroProvider:
             directory = self.root_dir + str(first_datetime.year)\
                         + "/" + str(first_datetime.month).zfill(2)\
                         + "/" + str(first_datetime.day).zfill(2)
+            if not os.path.exists(directory):
+                raise ValueError("No Picarro data available between " + first_datetime.strftime(utils.datetime_format) +
+                                 " and " + last_datetime.strftime(utils.datetime_format))
             filenames = os.listdir(directory)
 
             # TODO: Read only the relevant files, not all the files of the day.