diff --git a/src/CountriesMerger.py b/src/CountriesMerger.py
index 3f703ced405..92bbf85f31b 100644
--- a/src/CountriesMerger.py
+++ b/src/CountriesMerger.py
@@ -6,8 +6,7 @@ class CountriesMerger:
     @staticmethod
     def mergeSrcIntoDst(src: pd.Series, dst: pd.Series):
         def merge(series):
-            series = series.dropna()
-            return sorted(set().union(*series))
+            return sorted(set().union(*series.dropna()))
         
         mergedSeries = (pd
                         .merge(dst, src, how='left', left_index=True, right_index=True)