structs: fix interface{} type with map values

Fixes #76

structs.go

@@ -530,15 +530,22 @@ func (s *Struct) nested(val reflect.Value) interface{} {
 			finalVal = m
 		}
 	case reflect.Map:
-		v := val.Type().Elem()
-		if v.Kind() == reflect.Ptr {
-			v = v.Elem()
+		// get the element type of the map
+		mapElem := val.Type()
+		switch val.Type().Kind() {
+		case reflect.Ptr, reflect.Array, reflect.Map,
+			reflect.Slice, reflect.Chan:
+			mapElem = val.Type().Elem()
+			if mapElem.Kind() == reflect.Ptr {
+				mapElem = mapElem.Elem()
+			}
 		}
 
 		// only iterate over struct types, ie: map[string]StructType,
 		// map[string][]StructType,
-		if v.Kind() == reflect.Struct ||
-			(v.Kind() == reflect.Slice && v.Elem().Kind() == reflect.Struct) {
+		if mapElem.Kind() == reflect.Struct ||
+			(mapElem.Kind() == reflect.Slice &&
+				mapElem.Elem().Kind() == reflect.Struct) {
 			m := make(map[string]interface{}, val.Len())
 			for _, k := range val.MapKeys() {
 				m[k.String()] = s.nested(val.MapIndex(k))
@@ -558,6 +565,7 @@ func (s *Struct) nested(val reflect.Value) interface{} {
 		// TODO(arslan): should this be optional?
 		// do not iterate of non struct types, just pass the value. Ie: []int,
 		// []string, co... We only iterate further if it's a struct.
+		// i.e []foo or []*foo
 		if val.Type().Elem().Kind() != reflect.Struct &&
 			!(val.Type().Elem().Kind() == reflect.Ptr &&
 				val.Type().Elem().Elem().Kind() == reflect.Struct) {

structs_test.go

@@ -1426,3 +1426,28 @@ func TestPointer2Pointer(t *testing.T) {
 	c := &b
 	_ = Map(&c)
 }
+
+func TestMap_InterfaceTypeWithMapValue(t *testing.T) {
+	type A struct {
+		Name    string      `structs:"name"`
+		Ip      string      `structs:"ip"`
+		Query   string      `structs:"query"`
+		Payload interface{} `structs:"payload"`
+	}
+
+	a := A{
+		Name:    "test",
+		Ip:      "127.0.0.1",
+		Query:   "",
+		Payload: map[string]string{"test_param": "test_param"},
+	}
+
+	defer func() {
+		err := recover()
+		if err != nil {
+			t.Error("Converting Map with an interface{} type with map value should not panic")
+		}
+	}()
+
+	_ = Map(a)
+}