diff --git a/annif/backend/backend.py b/annif/backend/backend.py
index 6409c40fb..b1da11c7c 100644
--- a/annif/backend/backend.py
+++ b/annif/backend/backend.py
@@ -39,7 +39,7 @@ def suggest(self, text, project, params=None):
         """Suggest subjects for the input text and return a list of subjects
         represented as a list of SubjectSuggestion objects."""
         beparams = dict(self.params)
-        if params is not None:
+        if params:
             beparams.update(params)
         return self._suggest(text, project, params=beparams)