diff --git a/internal/querynodev2/tasks/task.go b/internal/querynodev2/tasks/search_task.go
similarity index 90%
rename from internal/querynodev2/tasks/task.go
rename to internal/querynodev2/tasks/search_task.go
index 774678dd39..90e9be6aea 100644
--- a/internal/querynodev2/tasks/task.go
+++ b/internal/querynodev2/tasks/search_task.go
@@ -130,7 +130,10 @@ func (t *SearchTask) Execute() error {
 	tr := timerecord.NewTimeRecorderWithTrace(t.ctx, "SearchTask")
 
 	req := t.req
-	t.combinePlaceHolderGroups()
+	err := t.combinePlaceHolderGroups()
+	if err != nil {
+		return err
+	}
 	searchReq, err := segments.NewSearchRequest(t.ctx, t.collection, req, t.placeholderGroup)
 	if err != nil {
 		return err
@@ -333,15 +336,28 @@ func (t *SearchTask) MergeWith(other Task) bool {
 }
 
 // combinePlaceHolderGroups combine all the placeholder groups.
-func (t *SearchTask) combinePlaceHolderGroups() {
-	if len(t.others) > 0 {
-		ret := &commonpb.PlaceholderGroup{}
-		_ = proto.Unmarshal(t.placeholderGroup, ret)
-		for _, t := range t.others {
-			x := &commonpb.PlaceholderGroup{}
-			_ = proto.Unmarshal(t.placeholderGroup, x)
-			ret.Placeholders[0].Values = append(ret.Placeholders[0].Values, x.Placeholders[0].Values...)
-		}
-		t.placeholderGroup, _ = proto.Marshal(ret)
+func (t *SearchTask) combinePlaceHolderGroups() error {
+	if len(t.others) == 0 {
+		return nil
 	}
+
+	ret := &commonpb.PlaceholderGroup{}
+	if err := proto.Unmarshal(t.placeholderGroup, ret); err != nil {
+		return merr.WrapErrParameterInvalidMsg("invalid search vector placeholder: %v", err)
+	}
+	if len(ret.GetPlaceholders()) == 0 {
+		return merr.WrapErrParameterInvalidMsg("empty search vector is not allowed")
+	}
+	for _, t := range t.others {
+		x := &commonpb.PlaceholderGroup{}
+		if err := proto.Unmarshal(t.placeholderGroup, x); err != nil {
+			return merr.WrapErrParameterInvalidMsg("invalid search vector placeholder: %v", err)
+		}
+		if len(x.GetPlaceholders()) == 0 {
+			return merr.WrapErrParameterInvalidMsg("empty search vector is not allowed")
+		}
+		ret.Placeholders[0].Values = append(ret.Placeholders[0].Values, x.Placeholders[0].Values...)
+	}
+	t.placeholderGroup, _ = proto.Marshal(ret)
+	return nil
 }
diff --git a/internal/querynodev2/tasks/search_task_test.go b/internal/querynodev2/tasks/search_task_test.go
new file mode 100644
index 0000000000..433fade9b6
--- /dev/null
+++ b/internal/querynodev2/tasks/search_task_test.go
@@ -0,0 +1,147 @@
+// Licensed to the LF AI & Data foundation under one
+// or more contributor license agreements. See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership. The ASF licenses this file
+// to you 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 tasks
+
+import (
+	"bytes"
+	"encoding/binary"
+	"math/rand"
+	"testing"
+
+	"github.com/golang/protobuf/proto"
+	"github.com/samber/lo"
+	"github.com/stretchr/testify/suite"
+
+	"github.com/milvus-io/milvus-proto/go-api/v2/commonpb"
+	"github.com/milvus-io/milvus/pkg/common"
+)
+
+type SearchTaskSuite struct {
+	suite.Suite
+}
+
+func (s *SearchTaskSuite) composePlaceholderGroup(nq int, dim int) []byte {
+	placeHolderGroup := &commonpb.PlaceholderGroup{
+		Placeholders: []*commonpb.PlaceholderValue{
+			{
+				Tag:  "$0",
+				Type: commonpb.PlaceholderType_FloatVector,
+				Values: lo.RepeatBy(nq, func(_ int) []byte {
+					bs := make([]byte, 0, dim*4)
+					for j := 0; j < dim; j++ {
+						var buffer bytes.Buffer
+						f := rand.Float32()
+						err := binary.Write(&buffer, common.Endian, f)
+						s.Require().NoError(err)
+						bs = append(bs, buffer.Bytes()...)
+					}
+					return bs
+				}),
+			},
+		},
+	}
+
+	bs, err := proto.Marshal(placeHolderGroup)
+	s.Require().NoError(err)
+	return bs
+}
+
+func (s *SearchTaskSuite) composeEmptyPlaceholderGroup() []byte {
+	placeHolderGroup := &commonpb.PlaceholderGroup{}
+
+	bs, err := proto.Marshal(placeHolderGroup)
+	s.Require().NoError(err)
+	return bs
+}
+
+func (s *SearchTaskSuite) TestCombinePlaceHolderGroups() {
+	s.Run("normal", func() {
+		task := &SearchTask{
+			placeholderGroup: s.composePlaceholderGroup(1, 128),
+			others: []*SearchTask{
+				{
+					placeholderGroup: s.composePlaceholderGroup(1, 128),
+				},
+			},
+		}
+
+		task.combinePlaceHolderGroups()
+	})
+
+	s.Run("tasked_not_merged", func() {
+		task := &SearchTask{}
+
+		err := task.combinePlaceHolderGroups()
+		s.NoError(err)
+	})
+
+	s.Run("empty_placeholdergroup", func() {
+		task := &SearchTask{
+			placeholderGroup: s.composeEmptyPlaceholderGroup(),
+			others: []*SearchTask{
+				{
+					placeholderGroup: s.composePlaceholderGroup(1, 128),
+				},
+			},
+		}
+
+		err := task.combinePlaceHolderGroups()
+		s.Error(err)
+
+		task = &SearchTask{
+			placeholderGroup: s.composePlaceholderGroup(1, 128),
+			others: []*SearchTask{
+				{
+					placeholderGroup: s.composeEmptyPlaceholderGroup(),
+				},
+			},
+		}
+
+		err = task.combinePlaceHolderGroups()
+		s.Error(err)
+	})
+
+	s.Run("unmarshal_fail", func() {
+		task := &SearchTask{
+			placeholderGroup: []byte{0x12, 0x34},
+			others: []*SearchTask{
+				{
+					placeholderGroup: s.composePlaceholderGroup(1, 128),
+				},
+			},
+		}
+
+		err := task.combinePlaceHolderGroups()
+		s.Error(err)
+
+		task = &SearchTask{
+			placeholderGroup: s.composePlaceholderGroup(1, 128),
+			others: []*SearchTask{
+				{
+					placeholderGroup: []byte{0x12, 0x34},
+				},
+			},
+		}
+
+		err = task.combinePlaceHolderGroups()
+		s.Error(err)
+	})
+}
+
+func TestSearchTask(t *testing.T) {
+	suite.Run(t, new(SearchTaskSuite))
+}