Add support to config for setting and writing blank values

internal/yamlmap/yaml_map.go

@@ -35,6 +35,13 @@ func MapValue() *Map {
 	}}
 }
 
+func NullValue() *Map {
+	return &Map{&yaml.Node{
+		Kind: yaml.ScalarNode,
+		Tag:  "!!null",
+	}}
+}
+
 func Unmarshal(data []byte) (*Map, error) {
 	var root yaml.Node
 	err := yaml.Unmarshal(data, &root)

pkg/config/config.go

@@ -102,7 +102,12 @@ func (c *Config) Remove(keys []string) error {
 // Set a string value in a Config.
 // The keys argument is a sequence of key values so that nested
 // entries can be set. If any of the keys do not exist they will
-// be created.
+// be created. If the string value to be set is empty it will be
+// represented as null not an empty string when written.
+//
+//	var c *Config
+//	c.Set([]string{"key"}, "")
+//	Write(c) // writes `key: ` not `key: ""`
 func (c *Config) Set(keys []string, value string) {
 	c.mu.Lock()
 	defer c.mu.Unlock()
@@ -116,7 +121,11 @@ func (c *Config) Set(keys []string, value string) {
 		}
 		m = entry
 	}
-	m.SetEntry(keys[len(keys)-1], yamlmap.StringValue(value))
+	val := yamlmap.StringValue(value)
+	if value == "" {
+		val = yamlmap.NullValue()
+	}
+	m.SetEntry(keys[len(keys)-1], val)
 }
 
 func (c *Config) deepCopy() *Config {

pkg/config/config_test.go

@@ -406,6 +406,18 @@ func TestWrite(t *testing.T) {
 	}
 }
 
+func TestWriteEmptyValues(t *testing.T) {
+	tempDir := t.TempDir()
+	t.Setenv("GH_CONFIG_DIR", tempDir)
+	cfg := ReadFromString(testFullConfig())
+	cfg.Set([]string{"editor"}, "")
+	err := Write(cfg)
+	assert.NoError(t, err)
+	data, err := os.ReadFile(generalConfigFile())
+	assert.NoError(t, err)
+	assert.Equal(t, "git_protocol: ssh\neditor:\nprompt: enabled\npager: less\n", string(data))
+}
+
 func TestGet(t *testing.T) {
 	tests := []struct {
 		name      string
@@ -595,6 +607,11 @@ func TestSet(t *testing.T) {
 			keys:  []string{"johnny", "test"},
 			value: "dukey",
 		},
+		{
+			name:  "set empty value",
+			keys:  []string{"empty"},
+			value: "",
+		},
 	}
 
 	for _, tt := range tests {