Fixes lp#1789415: Deal with nil value for 'juju config <app> <setting>'.

cmd/juju/application/config.go

@@ -364,7 +364,11 @@ func (c *configCommand) getConfig(client applicationAPI, ctx *cmd.Context) error
 		if !found {
 			return errors.Errorf("key %q not found in %q application config or charm settings.", key, c.applicationName)
 		}
-		fmt.Fprintln(ctx.Stdout, info["value"])
+		v, ok := info["value"]
+		if !ok || v == nil {
+			v = ""
+		}
+		fmt.Fprintln(ctx.Stdout, v)
 		return nil
 	}
 

featuretests/application_config_test.go

@@ -31,9 +31,7 @@ type ApplicationConfigSuite struct {
 	settingKeys set.Strings
 }
 
-func (s *ApplicationConfigSuite) SetUpTest(c *gc.C) {
-	s.JujuConnSuite.SetUpTest(c)
-
+func (s *ApplicationConfigSuite) assertApplicationDeployed(c *gc.C) {
 	// Create application with all available config field types [currently string, int, boolean, float]
 	// where each type has 3 settings:
 	// * one with a default;
@@ -104,6 +102,7 @@ func (s *ApplicationConfigSuite) getHookOutput(c *gc.C) charm.Settings {
 // since the logic and expected output is equivalent, these should be modified in sync.
 func (s *ApplicationConfigSuite) TestConfigAndConfigGetReturnAllCharmSettings(c *gc.C) {
 	// initial deploy with custom settings
+	s.assertApplicationDeployed(c)
 	s.assertSameConfigOutput(c, initialConfig)
 
 	// use 'juju config foo=' to change values
@@ -131,6 +130,26 @@ func (s *ApplicationConfigSuite) TestConfigAndConfigGetReturnAllCharmSettings(c
 	s.assertSameConfigOutput(c, resetConfig)
 }
 
+func (s *ApplicationConfigSuite) TestConfigNoValueSingleSetting(c *gc.C) {
+	appName := "appconfigsingle"
+	charm := s.AddTestingCharm(c, appName)
+	_, err := s.State.AddApplication(state.AddApplicationArgs{
+		Name:  appName,
+		Charm: charm,
+	})
+	c.Assert(err, jc.ErrorIsNil)
+	var options []string
+	for k := range charm.Config().Options {
+		options = append(options, k)
+	}
+	for i, option := range options {
+		c.Logf("case %d: 'juju config %v %v'", i, appName, option)
+		// use 'juju config foo' to see values
+		output := s.configCommandOutput(c, appName, option)
+		c.Assert(output, gc.Equals, "\n")
+	}
+}
+
 func (s *ApplicationConfigSuite) assertSameConfigOutput(c *gc.C, expectedValues settingsMap) {
 	s.assertJujuConfigOutput(c, s.configCommandOutput(c, s.appName), expectedValues)
 	s.assertHookOutput(c, s.getHookOutput(c), expectedValues)

testcharms/charm-repo/quantal/appconfigsingle/config.yaml

@@ -0,0 +1,21 @@
+options:
+  strnildefault:
+    default:
+    description: A string setting for charm with nil default value.
+    type: string
+  stremptydefault:
+    default: ""
+    description: A string settings for charm with empty default value.
+    type: string
+  intnildefault:
+    default:
+    description: An int setting for charm with nil default value.
+    type: int
+  floatnildefault:
+    default:
+    description: A float setting for charm with nil default value.
+    type: float
+  booleannildefault:
+    default:
+    description: A boolean setting for charm with nil default value.
+    type: boolean

testcharms/charm-repo/quantal/appconfigsingle/hooks/install

@@ -0,0 +1,2 @@
+#!/bin/bash
+echo "Done!"

testcharms/charm-repo/quantal/appconfigsingle/metadata.yaml

@@ -0,0 +1,5 @@
+name: appconfigsingle
+summary: "That's a charm with config settings that contain empty or nil default values to test 'juju config' ouput for a single setting."
+description: |
+    A very tricky charm.
+minjujuversion: "1.0.0"

testcharms/charm-repo/quantal/appconfigsingle/revision

@@ -0,0 +1 @@
+1