- Issue #17012: shutil.which() no longer fallbacks to the PATH environment

variable if empty path argument is specified.  Patch by Serhiy Storchaka.

Lib/shutil.py

@@ -1090,7 +1090,11 @@ def which(cmd, mode=os.F_OK | os.X_OK, path=None):
             return cmd
         return None
 
-    path = (path or os.environ.get("PATH", os.defpath)).split(os.pathsep)
+    if path is None:
+        path = os.environ.get("PATH", os.defpath)
+    if not path:
+        return None
+    path = path.split(os.pathsep)
 
     if sys.platform == "win32":
         # The current directory takes precedence on Windows.