diff --git a/expression/builtin_string_vec.go b/expression/builtin_string_vec.go
index 5f51caefa7fec..62c123faf07bd 100644
--- a/expression/builtin_string_vec.go
+++ b/expression/builtin_string_vec.go
@@ -2287,7 +2287,6 @@ func (b *builtinCharSig) vecEvalString(input *chunk.Chunk, result *chunk.Column)
 		bigints = bigints[0:0]
 		for j := 0; j < l-1; j++ {
 			if buf[j].IsNull(i) {
-				result.AppendNull()
 				continue
 			}
 			bigints = append(bigints, bufint[j][i])
diff --git a/expression/builtin_string_vec_test.go b/expression/builtin_string_vec_test.go
index fdb7868ccb2fd..13bfb384e10ea 100644
--- a/expression/builtin_string_vec_test.go
+++ b/expression/builtin_string_vec_test.go
@@ -330,6 +330,12 @@ var vecBuiltinStringCases = map[string][]vecExprBenchCase{
 			geners:        []dataGenerator{&charInt64Gener{}, &charInt64Gener{}, &charInt64Gener{}, nil},
 			constants:     []*Constant{nil, nil, nil, {Value: types.NewDatum("ascii"), RetType: types.NewFieldType(mysql.TypeString)}},
 		},
+		{
+			retEvalType:   types.ETString,
+			childrenTypes: []types.EvalType{types.ETInt, types.ETInt, types.ETInt, types.ETString},
+			geners:        []dataGenerator{&charInt64Gener{}, nil, &charInt64Gener{}, nil},
+			constants:     []*Constant{nil, nil, nil, {Value: types.NewDatum("ascii"), RetType: types.NewFieldType(mysql.TypeString)}},
+		},
 	},
 	ast.FindInSet: {
 		{retEvalType: types.ETInt, childrenTypes: []types.EvalType{types.ETString, types.ETString}},
diff --git a/expression/integration_test.go b/expression/integration_test.go
index d3c561e3340b4..7f01c659c126d 100644
--- a/expression/integration_test.go
+++ b/expression/integration_test.go
@@ -10649,6 +10649,18 @@ func (s *testIntegrationSuite) TestIssue29513(c *C) {
 	tk.MustQuery("select '123' union select cast(a as char(2)) from t;").Sort().Check(testkit.Rows("123", "45"))
 }
 
+func (s *testIntegrationSuite) TestIssue29755(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+
+	tk.MustExec("set tidb_enable_vectorized_expression = on;")
+	tk.MustQuery("select char(123, NULL, 123)").Check(testkit.Rows("{{"))
+	tk.MustQuery("select char(NULL, 123, 123)").Check(testkit.Rows("{{"))
+	tk.MustExec("set tidb_enable_vectorized_expression = off;")
+	tk.MustQuery("select char(123, NULL, 123)").Check(testkit.Rows("{{"))
+	tk.MustQuery("select char(NULL, 123, 123)").Check(testkit.Rows("{{"))
+}
+
 func (s *testIntegrationSuite) TestIssue30101(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	tk.MustExec("use test")