Fix isnull error in SeasonLookup.prepare_lookup_df - see HEA-787

Author: rhunwicks

apps/metadata/lookups.py

@@ -62,7 +62,7 @@ def prepare_lookup_df(self) -> pd.DataFrame:
         extra_dfs = []
         for country in all_countries:
             country_df = df[df["country_id"] == country]
-            null_purpose_rows = country_df[country_df["purpose"].isnull()]
+            null_purpose_rows = country_df[country_df["purpose"] == ""]
             for purpose in all_purposes:
                 # Only add duplicate rows for purposes that aren't already defined for this country
                 if purpose not in country_df["purpose"].unique():