Return nil on empty sink

pkg/commands/flags/sink.go

@@ -102,6 +102,10 @@ func (i *SinkFlags) Parse(namespace string) (*sink.Reference, error) {
 func (i *SinkFlags) ResolveSink(ctx context.Context, knclient clientdynamic.KnDynamicClient, namespace string) (*duckv1.Destination, error) {
 	s, err := i.Parse(namespace)
 	if err != nil {
+		if errors.Is(err, sink.ErrSinkIsRequired) {
+			// returns nil, if sink isn't provided to keep the current contract
+			return nil, nil
+		}
 		return nil, err
 	}
 	var dest *duckv1.Destination

pkg/commands/flags/sink_test.go

@@ -161,6 +161,7 @@ func TestResolve(t *testing.T) {
 			Name:       "foo",
 		}}, ""},
 		{"absent:foo", nil, "absents \"foo\" not found"},
+		{"", nil, ""},
 	}
 	dynamicClient := dynamicfake.CreateFakeKnDynamicClient(
 		"default",
@@ -171,11 +172,12 @@ func TestResolve(t *testing.T) {
 		t.Run(c.sink, func(t *testing.T) {
 			sf := &flags.SinkFlags{Sink: c.sink}
 			result, err := sf.ResolveSink(context.Background(), dynamicClient, "default")
-			if c.destination != nil {
+			if c.errContents == "" {
 				assert.DeepEqual(t, result, c.destination)
 				assert.NilError(t, err)
-				assert.Equal(t, c.errContents, "")
 			} else {
+				assert.Check(t, err != nil && err.Error() != "",
+					"error ins't empty")
 				assert.ErrorContains(t, err, c.errContents)
 			}
 		})

pkg/util/errors/cause_test.go

@@ -0,0 +1,36 @@
+/*
+ Copyright 2024 The Knative Authors
+
+ Licensed under the Apache License, Version 2.0 (the "License");
+ you may not use this file except in compliance with the License.
+ You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+*/
+
+package errors_test
+
+import (
+	"fmt"
+	"syscall"
+	"testing"
+
+	"knative.dev/client/pkg/util/errors"
+)
+
+func TestCauseOf(t *testing.T) {
+	errExample := errors.New("example error")
+	want := syscall.EINVAL
+	err := fmt.Errorf("%w: %w", errExample, want)
+
+	got := errors.CauseOf(err, errExample)
+	if !errors.Is(got, want) {
+		t.Errorf("got error %v, want %v", got, want)
+	}
+}

pkg/util/errors/wrap.go

@@ -0,0 +1,32 @@
+/*
+ Copyright 2024 The Knative Authors
+
+ Licensed under the Apache License, Version 2.0 (the "License");
+ you may not use this file except in compliance with the License.
+ You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+*/
+
+package errors
+
+import "emperror.dev/errors"
+
+// Is reports whether any error in err's chain matches target.
+//
+// An error is considered to match a target if it is equal to that target or if
+// it implements a method Is(error) bool such that Is(target) returns true.
+func Is(err, target error) bool {
+	return errors.Is(err, target)
+}
+
+// New returns a new error annotated with stack trace at the point New is called.
+func New(msg string) error {
+	return errors.New(msg)
+}