correction of repr when EddiesObservation is empty

Author: ludwigVonKoopa

CHANGELOG.rst

@@ -17,6 +17,7 @@ Changed
 Fixed
 ^^^^^
 - Use `safe_load` for yaml load
+- repr of EddiesObservation when the collection is empty (time attribute empty array)
 
 Added
 ^^^^^

src/py_eddy_tracker/observations/observation.py

@@ -2117,13 +2117,16 @@ def interp_grid(
     @property
     def period(self):
         """
-        Give the time coverage
+        Give the time coverage. If collection is empty, return nan,nan
 
         :return: first and last date
         :rtype: (int,int)
         """
         if self.period_ is None:
-            self.period_ = self.time.min(), self.time.max()
+            if self.time.size < 1:
+                self.period_ = nan, nan
+            else:
+                self.period_ = self.time.min(), self.time.max()
         return self.period_
 
     @property