contrib/gorm.io/gorm.v1: do not panic on open

If passing a nil `*gorm.Config` to `Open`, we should not panic, but instead
pass nothing on to `gorm`.

Fixes #2559

contrib/gorm.io/gorm.v1/gorm.go

@@ -36,7 +36,13 @@ const (
 // Open opens a new (traced) database connection. The used driver must be formerly registered
 // using (gopkg.in/DataDog/dd-trace-go.v1/contrib/database/sql).Register.
 func Open(dialector gorm.Dialector, cfg *gorm.Config, opts ...Option) (*gorm.DB, error) {
-	db, err := gorm.Open(dialector, cfg)
+	var db *gorm.DB
+	var err error
+	if cfg != nil {
+		db, err = gorm.Open(dialector, cfg)
+	} else {
+		db, err = gorm.Open(dialector)
+	}
 	if err != nil {
 		return db, err
 	}

contrib/gorm.io/gorm.v1/gorm_test.go

@@ -50,6 +50,19 @@ func TestMain(m *testing.M) {
 	os.Exit(testResult)
 }
 
+func TestOpenDoesNotPanic(t *testing.T) {
+	defer func() {
+		if r := recover(); r != nil {
+			assert.Fail(t, "Opening connection panicked", r)
+		}
+	}()
+	// None of the following calls should end up in a panic.
+	_, _ = gorm.Open(nil, &gorm.Config{})
+	_, _ = gorm.Open(nil, nil)
+	_, _ = Open(nil, &gorm.Config{})
+	_, _ = Open(nil, nil)
+}
+
 func TestMySQL(t *testing.T) {
 	sqltrace.Register("mysql", &mysql.MySQLDriver{}, sqltrace.WithServiceName("mysql-test"))
 	sqlDb, err := sqltrace.Open("mysql", mysqlConnString)