Protect against nil return objects

db/db.go

@@ -652,8 +652,10 @@ func (db *DB) executeStmtWithConn(ctx context.Context, stmt *command.Statement,
 	defer func() {
 		if retErr != nil {
 			retErr = rewriteContextTimeout(retErr, ErrExecuteTimeout)
+			if res != nil {
 				res.Error = retErr.Error()
 			}
+		}
 	}()
 	result := &command.ExecuteResult{}
 	start := time.Now()
@@ -813,8 +815,10 @@ func (db *DB) queryStmtWithConn(ctx context.Context, stmt *command.Statement, xT
 	defer func() {
 		if retErr != nil {
 			retErr = rewriteContextTimeout(retErr, ErrQueryTimeout)
+			if retRows != nil {
 				retRows.Error = retErr.Error()
 			}
+		}
 	}()
 	rows := &command.QueryRows{}
 	start := time.Now()