fix merge

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

file.go

@@ -7,6 +7,7 @@ import (
 	"io/ioutil"
 	"os"
 
+	"github.com/imdario/mergo"
 	"github.com/unistack-org/micro/v3/codec"
 	"github.com/unistack-org/micro/v3/config"
 )
@@ -62,7 +63,13 @@ func (c *fileConfig) Load(ctx context.Context) error {
 		var buf []byte
 		buf, err = ioutil.ReadAll(io.LimitReader(fp, int64(codec.DefaultMaxMsgSize)))
 		if err == nil {
-			err = c.opts.Codec.Unmarshal(buf, c.opts.Struct)
+			src, err := config.Zero(c.opts.Struct)
+			if err == nil {
+				err = c.opts.Codec.Unmarshal(buf, src)
+				if err == nil {
+					err = mergo.Merge(c.opts.Struct, src, mergo.WithOverride, mergo.WithTypeCheck, mergo.WithAppendSlice)
+				}
+			}
 		}
 		if err != nil && !c.opts.AllowFail {
 			return err