Merge pull request #146 from PyPSA/future-warning-map_bus

export: re-address future warning

Author: FabianHofmann

powerplantmatching/export.py

@@ -73,7 +73,11 @@ def map_bus(df, buses):
     """
     df = get_obj_if_Acc(df)
     kdtree = KDTree(buses[["x", "y"]])
-    buses_i = buses.index.append(pd.Index([np.nan]))
+    non_empty_buses = buses.dropna()
+    if non_empty_buses.empty:
+        buses_i = pd.Index([np.nan])
+    else:
+        buses_i = non_empty_buses.index.append(pd.Index([np.nan]))
     return df.assign(bus=buses_i[kdtree.query(df[["lon", "lat"]].values)[1]])