Avoid setting None in Path objects -- fix unit tests

Author: cderici

juju/utils.py

@@ -47,16 +47,15 @@ def juju_config_dir():
     * ~/.local/share/juju
 
     """
-    # Check $JUJU_DATA first
-    config_dir = Path(os.environ.get('JUJU_DATA', None))
-
-    # Second option: $XDG_DATA_HOME for ~/.local/share
-    if not config_dir.exists():
-        config_dir = Path(os.environ.get('XDG_DATA_HOME', '')) / 'juju'
-
-    # Third option: just set it to ~/.local/share/juju
-    if not config_dir.exists():
-        config_dir = Path('~/.local/share/juju')
+    # Set it to ~/.local/share/juju as default
+    config_dir = Path('~/.local/share/juju')
+
+    # Check $JUJU_DATA
+    if juju_data := os.environ.get('JUJU_DATA'):
+        config_dir = Path(juju_data)
+    # Secondly check: $XDG_DATA_HOME for ~/.local/share
+    elif xdg_data_home := os.environ.get('XDG_DATA_HOME'):
+        config_dir = Path(xdg_data_home) / 'juju'
 
     return str(config_dir.expanduser().resolve())