--- a/src/pyams_thesaurus/thesaurus.py	Tue Jul 10 16:57:58 2018 +0200
+++ b/src/pyams_thesaurus/thesaurus.py	Wed Jul 11 10:18:34 2018 +0200
@@ -203,7 +203,7 @@
                           if (not term.generic) and (not term.usage)]
 
     def get_top_terms(self, extract=None):
-        if extract is None:
+        if not extract:
             return self.top_terms
         return [term for term in self.top_terms if extract in term.extracts]