Fix/ Allow empty TimeSeries (#1359)

* removed the assert preventing TimeSeries to be empty, updated the associated test and the docstring
* added support for plotting empty TimeSeries

Author: madtoinou

darts/tests/test_logging.py

@@ -63,7 +63,7 @@ def test_timeseries_constructor_error_log(self):
             (
                 "darts.timeseries",
                 "ERROR",
-                "ValueError: The time series array must not be empty.",
+                "ValueError: TimeSeries require DataArray of dimensionality 3 (('time', 'component', 'sample')).",
             )
         )
 

darts/timeseries.py

@@ -22,7 +22,6 @@
     - Contain numeric types only
     - Have distinct components/columns names
     - Have a well defined frequency (for ``DateTimeIndex``)
-    - Be non-empty
     - Have static covariates consistent with their components, or no static covariates
     - Have a hierarchy consistent with their components, or no hierarchy
 
@@ -86,7 +85,6 @@ def __init__(self, xa: xr.DataArray):
             "TimeSeries.from_times_and_values(), etc...).",
             logger,
         )
-        raise_if_not(xa.size > 0, "The time series array must not be empty.", logger)
         raise_if_not(
             len(xa.shape) == 3,
             f"TimeSeries require DataArray of dimensionality 3 ({DIMS}).",
@@ -3230,6 +3228,15 @@ def plot(
 
             if central_series.shape[0] > 1:
                 p = central_series.plot(*args, **kwargs)
+            # empty TimeSeries
+            elif central_series.shape[0] == 0:
+                p = plt.plot(
+                    [],
+                    [],
+                    *args,
+                    **kwargs,
+                )
+                plt.xlabel(self.time_index.name)
             else:
                 p = plt.plot(
                     [self.start_time()],