Added correct notification for redownloading Slovenian models

Author: lkrsnik

classla/models/pos/postprocessor.py

@@ -198,6 +198,8 @@ def convert_feats(self, feats_string):
 
     def extract_lexicon_data(self, lexicon):
         """ Creates hypothesis dictionary from lexicon. """
+        if lexicon is None:
+            raise Exception("You have to re-download Slovenian models. You can do this by using the following command: classla.download('sl')")
         for key in lexicon:
             if key[1] in self.xpos_vocab:
                 self.hypothesis_dictionary_xpos.setdefault(key[0].lower(), []).append(key[1])