Changed policiesList and rolesList from declaration to definition to …

…fix nil error in encoding/json. golang/go#27589 (comment)

engine/ladon/handler.go

@@ -290,8 +290,7 @@ func (e *Engine) Register(r *httprouter.Router) {
 }
 
 func (e *Engine) rolesList(ctx context.Context, r *http.Request, ps httprouter.Params) (*kstorage.ListRequest, error) {
-	var p kstorage.Roles
-
+	p := make([]kstorage.Role, 0)
 	f, err := flavor(ps)
 	if err != nil {
 		return nil, err
@@ -428,8 +427,8 @@ func (e *Engine) policiesCreate(ctx context.Context, r *http.Request, ps httprou
 }
 
 func (e *Engine) policiesList(ctx context.Context, r *http.Request, ps httprouter.Params) (*kstorage.ListRequest, error) {
-	var p kstorage.Policies
 
+	p := make([]kstorage.Policy, 0)
 	f, err := flavor(ps)
 	if err != nil {
 		return nil, err

storage/handler.go

@@ -84,17 +84,17 @@ func (l *ListRequest) Filter(m map[string][]string) *ListRequest {
 
 func ListByQuery(l *ListRequest, m map[string][]string) {
 	switch val := l.Value.(type) {
-	case *Roles:
-		var res Roles
+	case *[]Role:
+		res := make([]Role, 0)
 		for _, role := range *val {
 			filteredRole := role.withMembers(m["member"]).withIDs(m["id"])
 			if filteredRole != nil {
 				res = append(res, *filteredRole)
 			}
 		}
 		l.Value = &res
-	case *Policies:
-		var res Policies
+	case *[]Policy:
+		res := make([]Policy, 0)
 		for _, policy := range *val {
 			filteredPolicy := policy.withSubjects(m["subject"]).withResources(m["resource"]).withActions(m["action"]).withIDs(m["id"])
 			if filteredPolicy != nil {