diff --git a/expression/builtin_convert_charset.go b/expression/builtin_convert_charset.go
index 9fafbd36f3117..91b8eb57b5f1d 100644
--- a/expression/builtin_convert_charset.go
+++ b/expression/builtin_convert_charset.go
@@ -322,7 +322,8 @@ func HandleBinaryLiteral(ctx sessionctx.Context, expr Expression, ec *ExprCollat
 				return expr
 			}
 			return BuildToBinaryFunction(ctx, expr)
-		} else if argChs == charset.CharsetBin && dstChs != charset.CharsetBin {
+		} else if argChs == charset.CharsetBin && dstChs != charset.CharsetBin &&
+			expr.GetType().GetType() != mysql.TypeNull {
 			ft := expr.GetType().Clone()
 			ft.SetCharset(ec.Charset)
 			ft.SetCollate(ec.Collation)
diff --git a/expression/integration_test.go b/expression/integration_test.go
index 4807cb22aa5d1..5e7942b61262c 100644
--- a/expression/integration_test.go
+++ b/expression/integration_test.go
@@ -7496,3 +7496,15 @@ func TestIssue41986(t *testing.T) {
 	// shouldn't report they can't find column error and return the right result.
 	tk.MustQuery("SELECT GROUP_CONCAT(effective_date order by stlmnt_hour DESC) FROM ( SELECT (COALESCE(pct.clearing_time, 0)/3600000) AS stlmnt_hour ,COALESCE(pct.effective_date, '1970-01-01 08:00:00') AS effective_date FROM poi_clearing_time_topic pct ORDER BY pct.effective_date DESC ) a;").Check(testkit.Rows("2023-08-25 00:00:00"))
 }
+
+func TestIssue49526(t *testing.T) {
+	store, clean := testkit.CreateMockStore(t)
+	defer clean()
+	tk := testkit.NewTestKit(t, store)
+
+	rows := tk.MustQuery("explain select null as a union all select 'a' as a;").Rows()
+	for _, r := range rows {
+		require.NotContains(t, r[4], "from_binary")
+	}
+	tk.MustQuery("select null as a union all select 'a' as a;").Sort().Check(testkit.Rows("<nil>", "a"))
+}
diff --git a/go.mod b/go.mod
index 60c69bb391fc2..d40b81f97ec4f 100644
--- a/go.mod
+++ b/go.mod
@@ -206,3 +206,10 @@ replace github.com/pingcap/tidb/parser => ./parser
 
 // fix potential security issue(CVE-2020-26160) introduced by indirect dependency.
 replace github.com/dgrijalva/jwt-go => github.com/form3tech-oss/jwt-go v3.2.6-0.20210809144907-32ab6a8243d7+incompatible
+
+replace (
+	// TODO: `sourcegraph.com/sourcegraph/appdash` has been archived, and the original host has been removed.
+	// Please remove these dependencies.
+	sourcegraph.com/sourcegraph/appdash => github.com/sourcegraph/appdash v0.0.0-20190731080439-ebfcffb1b5c0
+	sourcegraph.com/sourcegraph/appdash-data => github.com/sourcegraph/appdash-data v0.0.0-20151005221446-73f23eafcf67
+)
diff --git a/go.sum b/go.sum
index 59dd6b279d334..74bf81a418a49 100644
--- a/go.sum
+++ b/go.sum
@@ -729,6 +729,10 @@ github.com/soheilhy/cmux v0.1.4/go.mod h1:IM3LyeVVIOuxMH7sFAkER9+bJ4dT7Ms6E4xg4k
 github.com/soheilhy/cmux v0.1.5 h1:jjzc5WVemNEDTLwv9tlmemhC73tI08BNOIGwBOo10Js=
 github.com/soheilhy/cmux v0.1.5/go.mod h1:T7TcVDs9LWfQgPlPsdngu6I6QIoyIFZDDC6sNE1GqG0=
 github.com/spaolacci/murmur3 v0.0.0-20180118202830-f09979ecbc72/go.mod h1:JwIasOWyU6f++ZhiEuf87xNszmSA2myDM2Kzu9HwQUA=
+github.com/sourcegraph/appdash v0.0.0-20190731080439-ebfcffb1b5c0 h1:IJ3DuWHPTJrsqtIqjfdmPTELdTFGefvrOa2eTeRBleQ=
+github.com/sourcegraph/appdash v0.0.0-20190731080439-ebfcffb1b5c0/go.mod h1:V952P4GGl1v/MMynLwxVdWEbSZJx+n0oOO3ljnez+WU=
+github.com/sourcegraph/appdash-data v0.0.0-20151005221446-73f23eafcf67 h1:8ZnTA26bBOoPkAbbitKPgNlpw0Bwt7ZlpYgZWHWJR/w=
+github.com/sourcegraph/appdash-data v0.0.0-20151005221446-73f23eafcf67/go.mod h1:tNZjgbYncKL5HxvDULAr/mWDmFz4B7H8yrXEDlnoIiw=
 github.com/spf13/afero v1.1.2/go.mod h1:j4pytiNVoe2o6bmDsKpLACNPDBIoEAkihy7loJ1B0CQ=
 github.com/spf13/afero v1.2.2/go.mod h1:9ZxEEn6pIJ8Rxe320qSDBk6AsU0r9pR7Q4OcevTdifk=
 github.com/spf13/cast v1.3.0/go.mod h1:Qx5cxh0v+4UWYiBimWS+eyWzqEqokIECu5etghLkUJE=
@@ -1436,8 +1440,4 @@ rsc.io/pdf v0.1.1/go.mod h1:n8OzWcQ6Sp37PL01nO98y4iUCRdTGarVfzxY20ICaU4=
 rsc.io/quote/v3 v3.1.0/go.mod h1:yEA65RcK8LyAZtP9Kv3t0HmxON59tX3rD+tICJqUlj0=
 rsc.io/sampler v1.3.0/go.mod h1:T1hPZKmBbMNahiBKFy5HrXp6adAjACjK9JXDnKaTXpA=
 sigs.k8s.io/yaml v1.2.0 h1:kr/MCeFWJWTwyaHoR9c8EjH9OumOmoF9YGiZd7lFm/Q=
-sigs.k8s.io/yaml v1.2.0/go.mod h1:yfXDCHCao9+ENCvLSE62v9VSji2MKu5jeNfTrofGhJc=
-sourcegraph.com/sourcegraph/appdash v0.0.0-20190731080439-ebfcffb1b5c0 h1:ucqkfpjg9WzSUubAO62csmucvxl4/JeW3F4I4909XkM=
-sourcegraph.com/sourcegraph/appdash v0.0.0-20190731080439-ebfcffb1b5c0/go.mod h1:hI742Nqp5OhwiqlzhgfbWU4mW4yO10fP+LoT9WOswdU=
-sourcegraph.com/sourcegraph/appdash-data v0.0.0-20151005221446-73f23eafcf67 h1:e1sMhtVq9AfcEy8AXNb8eSg6gbzfdpYhoNqnPJa+GzI=
-sourcegraph.com/sourcegraph/appdash-data v0.0.0-20151005221446-73f23eafcf67/go.mod h1:L5q+DGLGOQFpo1snNEkLOJT2d1YTW66rWNzatr3He1k=
+sigs.k8s.io/yaml v1.2.0/go.mod h1:yfXDCHCao9+ENCvLSE62v9VSji2MKu5jeNfTrofGhJc=
\ No newline at end of file