add assertion

Author: rhayes777

autofit/aggregator/summary/aggregate_csv.py

@@ -190,6 +190,9 @@ def __init__(self, aggregator: Aggregator):
         ----------
         aggregator
         """
+        if len(aggregator) == 0:
+            raise ValueError("The aggregator is empty.")
+
         self._aggregator = aggregator
         self._columns = []
 

autofit/aggregator/summary/aggregate_fits.py

@@ -43,6 +43,9 @@ def __init__(self, aggregator: Aggregator):
         aggregator
             The aggregator containing the fits files.
         """
+        if len(aggregator) == 0:
+            raise ValueError("The aggregator is empty.")
+
         self.aggregator = aggregator
 
     @staticmethod