groupByLabel: empty string value is a valid group

Author: codekitchen

template.go

@@ -116,10 +116,10 @@ func groupByKeys(entries interface{}, key string) ([]string, error) {
 func groupByLabel(entries interface{}, label string) (map[string][]interface{}, error) {
 	getLabel := func(v interface{}) (interface{}, error) {
 		if container, ok := v.(RuntimeContainer); ok {
-			if container.Labels[label] == "" {
-				return nil, nil
+			if value, ok := container.Labels[label]; ok {
+				return value, nil
 			}
-			return container.Labels[label], nil
+			return nil, nil
 		}
 		return nil, fmt.Errorf("Must pass an array or slice of RuntimeContainer to 'groupByLabel'; received %v", v)
 	}

template_test.go

@@ -209,20 +209,29 @@ func TestGroupByLabel(t *testing.T) {
 		&RuntimeContainer{
 			ID: "4",
 		},
+		&RuntimeContainer{
+			Labels: map[string]string{
+				"com.docker.compose.project": "",
+			},
+			ID: "5",
+		},
 	}
 
 	groups, err := groupByLabel(containers, "com.docker.compose.project")
 	if err != nil {
 		t.FailNow()
 	}
 
-	if len(groups) != 2 {
+	if len(groups) != 3 {
 		t.Fail()
 	}
 
 	if len(groups["one"]) != 2 {
 		t.Fail()
 	}
+	if len(groups[""]) != 1 {
+		t.Fail()
+	}
 
 	if len(groups["two"]) != 1 {
 		t.FailNow()