Resolve "release v1.4.0"

Closes #317 (closed)

mlair/data_handler/data_handler_single_station.py

@@ -406,7 +406,8 @@ class DataHandlerSingleStation(AbstractDataHandler):
                      "propane", "so2", "toluene"]
         # used_chem_vars = list(set(chem_vars) & set(self.statistics_per_var.keys()))
         used_chem_vars = list(set(chem_vars) & set(data.variables.values))
-        data.loc[..., used_chem_vars] = data.loc[..., used_chem_vars].clip(min=minimum)
+        if len(used_chem_vars) > 0:
+            data.loc[..., used_chem_vars] = data.loc[..., used_chem_vars].clip(min=minimum)
         return data
 
     def setup_data_path(self, data_path: str, sampling: str):