[bugfix] Fix --show-config for null config options

reframe/core/runtime.py

@@ -162,13 +162,17 @@ def modules_system(self):
         '''
         return self._system.modules_system
 
-    def get_option(self, option):
+    def get_option(self, option, default=None):
         '''Get a configuration option.
 
         :arg option: The option to be retrieved.
+        :arg default: The value to return if ``option`` cannot be retrieved.
         :returns: The value of the option.
+
+        .. versionchanged:: 3.11.0
+          Add ``default`` named argument.
         '''
-        return self._site_config.get(option)
+        return self._site_config.get(option, default=default)
 
 
 # Global resources for the current host

reframe/frontend/cli.py

@@ -772,8 +772,11 @@ def restrict_logging():
         if config_param == 'all':
             printer.info(str(rt.site_config))
         else:
-            value = rt.get_option(config_param)
-            if value is None:
+            # Create a unique value to differentiate between configuration
+            # parameters with value `None` and invalid ones
+            default = {'token'}
+            value = rt.get_option(config_param, default)
+            if value is default:
                 printer.error(
                     f'no such configuration parameter found: {config_param}'
                 )

reframe/schemas/config.json

@@ -571,6 +571,7 @@
         "systems/partitions/max_jobs": 8,
         "systems/partitions/prepare_cmds": [],
         "systems/partitions/processor": {},
+        "systems/partitions/time_limit": null,
         "systems/partitions/devices": [],
         "systems/partitions/extras": {}
     }

unittests/test_cli.py

@@ -620,6 +620,17 @@ def test_show_config_unknown_param(run_reframe):
     assert returncode == 0
 
 
+def test_show_config_null_param(run_reframe):
+    returncode, stdout, stderr = run_reframe(
+        more_options=['--show-config=general/report_junit'],
+        system='testsys'
+    )
+    assert 'null' in stdout
+    assert 'Traceback' not in stdout
+    assert 'Traceback' not in stderr
+    assert returncode == 0
+
+
 def test_verbosity(run_reframe):
     returncode, stdout, stderr = run_reframe(
         more_options=['-vvvvv'],