diff --git a/tabula/io.py b/tabula/io.py
index ece7403..8bcc90e 100644
--- a/tabula/io.py
+++ b/tabula/io.py
@@ -415,7 +415,7 @@ def read_pdf(
         if temporary:
             os.unlink(path)
 
-    if len(output) == 0:
+    if not output:
         logger.warning("The output file is empty.")
         return []