diff --git a/backend/union/errors.go b/backend/union/errors.go
index 46259b595..ddfd2866d 100644
--- a/backend/union/errors.go
+++ b/backend/union/errors.go
@@ -49,8 +49,7 @@ func (e Errors) Error() string {
 
 	if len(e) == 0 {
 		buf.WriteString("no error")
-	}
-	if len(e) == 1 {
+	} else if len(e) == 1 {
 		buf.WriteString("1 error: ")
 	} else {
 		fmt.Fprintf(&buf, "%d errors: ", len(e))
@@ -61,8 +60,17 @@ func (e Errors) Error() string {
 			buf.WriteString("; ")
 		}
 
-		buf.WriteString(err.Error())
+		if err != nil {
+			buf.WriteString(err.Error())
+		} else {
+			buf.WriteString("nil error")
+		}
 	}
 
 	return buf.String()
 }
+
+// Unwrap returns the wrapped errors
+func (e Errors) Unwrap() []error {
+	return e
+}
diff --git a/backend/union/errors_test.go b/backend/union/errors_test.go
new file mode 100644
index 000000000..3d79a69b0
--- /dev/null
+++ b/backend/union/errors_test.go
@@ -0,0 +1,94 @@
+//go:build go1.20
+// +build go1.20
+
+package union
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+var (
+	err1 = errors.New("Error 1")
+	err2 = errors.New("Error 2")
+	err3 = errors.New("Error 3")
+)
+
+func TestErrorsMap(t *testing.T) {
+	es := Errors{
+		nil,
+		err1,
+		err2,
+	}
+	want := Errors{
+		err2,
+	}
+	got := es.Map(func(e error) error {
+		if e == err1 {
+			return nil
+		}
+		return e
+	})
+	assert.Equal(t, want, got)
+}
+
+func TestErrorsFilterNil(t *testing.T) {
+	es := Errors{
+		nil,
+		err1,
+		nil,
+		err2,
+		nil,
+	}
+	want := Errors{
+		err1,
+		err2,
+	}
+	got := es.FilterNil()
+	assert.Equal(t, want, got)
+}
+
+func TestErrorsErr(t *testing.T) {
+	// Check not all nil case
+	es := Errors{
+		nil,
+		err1,
+		nil,
+		err2,
+		nil,
+	}
+	want := Errors{
+		err1,
+		err2,
+	}
+	got := es.Err()
+
+	// Check all nil case
+	assert.Equal(t, want, got)
+	es = Errors{
+		nil,
+		nil,
+		nil,
+	}
+	assert.Nil(t, es.Err())
+}
+
+func TestErrorsError(t *testing.T) {
+	assert.Equal(t, "no error", Errors{}.Error())
+	assert.Equal(t, "1 error: Error 1", Errors{err1}.Error())
+	assert.Equal(t, "1 error: nil error", Errors{nil}.Error())
+	assert.Equal(t, "2 errors: Error 1; Error 2", Errors{err1, err2}.Error())
+}
+
+func TestErrorsUnwrap(t *testing.T) {
+	es := Errors{
+		err1,
+		err2,
+	}
+	assert.Equal(t, []error{err1, err2}, es.Unwrap())
+	assert.True(t, errors.Is(es, err1))
+	assert.True(t, errors.Is(es, err2))
+	assert.False(t, errors.Is(es, err3))
+}