cherry pick pingcap#37321 to release-6.1

Signed-off-by: ti-srebot <[email protected]>

session/tidb.go

@@ -49,11 +49,19 @@ type domainMap struct {
 }
 
 func (dm *domainMap) Get(store kv.Storage) (d *domain.Domain, err error) {
-	key := store.UUID()
-
 	dm.mu.Lock()
 	defer dm.mu.Unlock()
 
+	if store == nil {
+		for _, d := range dm.domains {
+			// return available domain if any
+			return d, nil
+		}
+		return nil, errors.New("can not find available domain for a nil store")
+	}
+
+	key := store.UUID()
+
 	d = dm.domains[key]
 	if d != nil {
 		return

session/tidb_test.go

@@ -26,6 +26,14 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+func TestDomapHandleNil(t *testing.T) {
+	// this is required for enterprise plugins
+	// ref: https://github.com/pingcap/tidb/issues/37319
+	require.NotPanics(t, func() {
+		_, _ = domap.Get(nil)
+	})
+}
+
 func TestSysSessionPoolGoroutineLeak(t *testing.T) {
 	store, dom := createStoreAndBootstrap(t)
 	defer func() { require.NoError(t, store.Close()) }()