Fix non-editable install

mpas_analysis/__main__.py

@@ -943,6 +943,9 @@ def get_editable_install_dir(package_name):
 
     direct_url = Distribution.from_name(package_name).read_text(
         'direct_url.json')
+    if direct_url is None:
+            return None
+
     contents = json.loads(direct_url)
     pkg_is_editable = contents.get("dir_info", {}).get("editable", False)
     if pkg_is_editable and 'url' in contents:

mpas_analysis/test/test_main.py

@@ -0,0 +1,36 @@
+# This software is open source software available under the BSD-3 license.
+#
+# Copyright (c) 2022 Triad National Security, LLC. All rights reserved.
+# Copyright (c) 2022 Lawrence Livermore National Security, LLC. All rights
+# reserved.
+# Copyright (c) 2022 UT-Battelle, LLC. All rights reserved.
+#
+# Additional copyright and license information can be found in the LICENSE file
+# distributed with this code, or at
+# https://raw.githubusercontent.com/MPAS-Dev/MPAS-Analysis/main/LICENSE
+"""
+Regression tests for helpers in ``mpas_analysis.__main__``.
+"""
+
+import os
+from unittest.mock import Mock, patch
+
+from mpas_analysis.test import TestCase
+
+
+# Importing mpas_analysis.__main__ triggers matplotlib imports in some test
+# environments, so use a writable cache directory.
+os.environ.setdefault('MPLCONFIGDIR', '/tmp/matplotlib')
+
+import mpas_analysis.__main__ as main
+
+
+class TestMain(TestCase):
+    def test_get_editable_install_dir_without_direct_url(self):
+        distribution = Mock()
+        distribution.read_text.return_value = None
+
+        with patch.object(main.Distribution, 'from_name',
+                          return_value=distribution):
+            self.assertEqual(main.get_editable_install_dir('mpas_analysis'),
+                             None)