fix lines plot: fix f string and include args in conditionals (#272)

Author: ctuguinay

echoregions/lines/lines.py

@@ -185,11 +185,11 @@ def plot(
             Additional arguments passed to matplotlib `plot` or `fill_between`.
             Useful arguments include `color`, `lw`, and `marker`.
         """
-        if not None and not (isinstance(start_time, Timestamp)):
-            raise TypeError(f"start time is of type {type(start_time)} \
+        if start_time is not None and not (isinstance(start_time, Timestamp)):
+            raise TypeError(f"Start time is of type {type(start_time)}. \
                             It must be of of type Pandas Timestamp.")
-        if not None and not (isinstance(end_time, Timestamp)):
-            raise TypeError(f"end time is of type {type(end_time)} \
+        if end_time is not None and not (isinstance(end_time, Timestamp)):
+            raise TypeError(f"End time is of type {type(end_time)}. \
                             It must be of of type Pandas Timestamp.")
 
         df = self.data