Clean up eject_device

src/calibre/devices/folder_device/driver.py

@@ -88,6 +88,9 @@ class FOLDER_DEVICE(USBMS):
     def get_main_ebook_dir(self):
         return ''
 
+    def eject(self):
+        self.is_connected = False
+
     @classmethod
     def settings(self):
         return FOLDER_DEVICE_FOR_CONFIG._config().parse()

src/calibre/devices/usbms/driver.py

@@ -248,6 +248,8 @@ class USBMS(CLI, Device):
 
     @classmethod
     def normalize_path(cls, path):
+        if path is None:
+            return None
         if os.sep == '\\':
             path = path.replace('/', '\\')
         else: