diff --git a/src/biocatalyzer/bioreactor.py b/src/biocatalyzer/bioreactor.py
index 4028648..0141502 100644
--- a/src/biocatalyzer/bioreactor.py
+++ b/src/biocatalyzer/bioreactor.py
@@ -498,7 +498,7 @@ def _match_conditions(self, smiles: str):
         bool
             True if mol matches conditions to remove, False otherwise.
         """
-        if not smiles:
+        if smiles is None:
             return False
         if '*' in smiles:
             return False