Handle nil environment (#154)

bundle/config/mutator/select_default_environment.go

@@ -33,8 +33,8 @@ func (m *selectDefaultEnvironment) Apply(_ context.Context, b *bundle.Bundle) ([
 
 	// Multiple environments means we look for the `default` flag.
 	var defaults []string
-	for _, name := range names {
-		if b.Config.Environments[name].Default {
+	for name, env := range b.Config.Environments {
+		if env != nil && env.Default {
 			defaults = append(defaults, name)
 		}
 	}

bundle/config/mutator/select_default_environment_test.go

@@ -48,6 +48,19 @@ func TestSelectDefaultEnvironmentNoDefaults(t *testing.T) {
 	assert.ErrorContains(t, err, "please specify environment")
 }
 
+func TestSelectDefaultEnvironmentNoDefaultsWithNil(t *testing.T) {
+	bundle := &bundle.Bundle{
+		Config: config.Root{
+			Environments: map[string]*config.Environment{
+				"foo": nil,
+				"bar": nil,
+			},
+		},
+	}
+	_, err := mutator.SelectDefaultEnvironment().Apply(context.Background(), bundle)
+	assert.ErrorContains(t, err, "please specify environment")
+}
+
 func TestSelectDefaultEnvironmentMultipleDefaults(t *testing.T) {
 	bundle := &bundle.Bundle{
 		Config: config.Root{

bundle/config/root.go

@@ -87,6 +87,11 @@ func (r *Root) Merge(other *Root) error {
 func (r *Root) MergeEnvironment(env *Environment) error {
 	var err error
 
+	// Environment may be nil if it's empty.
+	if env == nil {
+		return nil
+	}
+
 	if env.Bundle != nil {
 		err = mergo.MergeWithOverwrite(&r.Bundle, env.Bundle)
 		if err != nil {