Don't swallow error in SM patch and use new RNode Map method.

api/internal/wrappy/wnode_test.go

@@ -8,6 +8,7 @@ import (
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
+	"github.com/stretchr/testify/assert"
 	"gopkg.in/yaml.v3"
 	"sigs.k8s.io/kustomize/api/resid"
 	kyaml "sigs.k8s.io/kustomize/kyaml/yaml"
@@ -480,6 +481,10 @@ func TestGetSlice(t *testing.T) {
 	}
 }
 
+func TestMapEmpty(t *testing.T) {
+	assert.Equal(t, 0, len(NewWNode().Map()))
+}
+
 func TestMap(t *testing.T) {
 	wn := NewWNode()
 	if err := wn.UnmarshalJSON([]byte(deploymentLittleJson)); err != nil {