fix deserialization panics on empty map

internal/route/provider/file_test.go

@@ -0,0 +1,17 @@
+package provider
+
+import (
+	"testing"
+
+	_ "embed"
+
+	. "github.com/yusing/go-proxy/internal/utils/testing"
+)
+
+//go:embed all_fields.yaml
+var yaml []byte
+
+func TestFile(t *testing.T) {
+	_, err := validate(yaml)
+	ExpectNoError(t, err)
+}