get-models: Handle version == "" same as None

src/nctool/cli.py

@@ -70,7 +70,7 @@ def get_models(host, port, username, destination):
             assert any(
                 [el.text == "NETCONF" for el in schema.findall(prefix + "location")]
             )
-            if version is not None:
+            if version is not None and version != "":
                 v = f"@{version}"
             else:
                 v = ""