Implemented merging of pressure level and single level ERA5 datasets.

climax/core/dataset.py

@@ -108,7 +108,7 @@ class ERA5Dataset(EoDataset):
 
         # drop projection variable, if present
         predictors = [ds.drop_vars(PROJECTION) for ds in predictors if
-                      PROJECTION in predictors]
+                      PROJECTION in ds.data_vars]
 
         # merge final predictor dataset
         return xr.merge(predictors)