'or' logic doesn't allow 'None' which evaluates as False.

This means that "allow_agent" cannot be set to True
based on the logic provided.

Instead, check if the value exists in the dict, then
set the value absolutely (even if it's "None") if set.

lib/jnpr/junos/device.py

@@ -1146,10 +1146,14 @@ def __init__(self, *vargs, **kvargs):
             self._ssh_config = kvargs.get('ssh_config')
             self._sshconf_lkup()
             # but if user or private key is explicit from call, then use it.
-            self._auth_user = kvargs.get('user') or self._conf_auth_user or \
-                self._auth_user
-            self._ssh_private_key_file = kvargs.get('ssh_private_key_file') \
-                or self._conf_ssh_private_key_file
+            if 'user' in kvargs:
+                self._auth_user = kvargs.get('user')
+            else:
+                self._auth_user = self._conf_auth_user or self._auth_user
+            if 'ssh_private_key_file' in kvargs:
+                self._ssh_private_key_file = kvargs.get('ssh_private_key_file')
+            else:
+                self._ssh_private_key_file = self._conf_ssh_private_key_file
             self._auth_password = kvargs.get(
                 'password') or kvargs.get('passwd')