fix: no Unmarshal when json is empty (#5)

* fix: no Unmarshal when json is empty

* Update adapter.go

Co-authored-by: hsluoyz <hsluoyz@qq.com>

Author: yyy1000

adapter.go

@@ -56,6 +56,10 @@ func (a *Adapter) saveToBuffer() error {
 }
 
 func (a *Adapter) loadFromBuffer() error {
+	if len(*a.source) == 0 {
+		return nil
+	}
+
 	var policy []CasbinRule
 	err := json.Unmarshal(*a.source, &policy)
 	if err == nil {

go.mod

@@ -2,4 +2,4 @@ module github.com/casbin/json-adapter/v2
 
 go 1.12
 
-require github.com/casbin/casbin/v2 v2.0.0
+require github.com/casbin/casbin/v2 v2.60.0

go.sum

@@ -1,4 +1,12 @@
 github.com/Knetic/govaluate v3.0.1-0.20171022003610-9aa49832a739+incompatible h1:1G1pk05UrOh0NlF1oeaaix1x8XzrfjIDK47TY0Zehcw=
 github.com/Knetic/govaluate v3.0.1-0.20171022003610-9aa49832a739+incompatible/go.mod h1:r7JcOSlj0wfOMncg0iLm8Leh48TZaKVeNIfJntJ2wa0=
-github.com/casbin/casbin/v2 v2.0.0 h1:OIcnP8SxwF1gmGxOn7Kod/O/7yJikpHWQz0qiBJpG/U=
-github.com/casbin/casbin/v2 v2.0.0/go.mod h1:YcPU1XXisHhLzuxH9coDNf2FbKpjGlbCg3n9yuLkIJQ=
+github.com/casbin/casbin/v2 v2.60.0 h1:ZmC0/t4wolfEsDpDxTEsu2z6dfbMNpc11F52ceLs2Eo=
+github.com/casbin/casbin/v2 v2.60.0/go.mod h1:vByNa/Fchek0KZUgG5wEsl7iFsiviAYKRtgrQfcJqHg=
+github.com/golang/mock v1.4.4 h1:l75CXGRSwbaYNpl/Z2X1XIIAMSCquvXgpVZDhwEIJsc=
+github.com/golang/mock v1.4.4/go.mod h1:l3mdAwkq5BuhzHwde/uurv3sEJeZMXNpwsxVWU71h+4=
+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/net v0.0.0-20190311183353-d8887717615a/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/tools v0.0.0-20190425150028-36563e24a262/go.mod h1:RgjU9mgBXZiqYHBnxXauZ1Gv1EHHAz9KjViQ78xBX0Q=