message: op-batcher: better error handling logic
  Be extra pendantic around expected data being not `nil`
  to prevent unexpected panics.
diff: @@ -74,16 +74,19 @@ func (t *TransactionManager) calcGasTipAndFeeCap(ctx context.Context) (gasTipCap
  childCtx, cancel := context.WithTimeout(ctx, networkTimeout)
  gasTipCap, err = t.l1Client.SuggestGasTipCap(childCtx)
  cancel()
  - if err != nil {
  + if err != nil || gasTipCap == nil {
  return nil, nil, fmt.Errorf("failed to get suggested gas tip cap: %w", err)
  }
  childCtx, cancel = context.WithTimeout(ctx, networkTimeout)
  head, err := t.l1Client.HeaderByNumber(childCtx, nil)
  cancel()
  - if err != nil {
  + if err != nil || head == nil {
  return nil, nil, fmt.Errorf("failed to get L1 head block for fee cap: %w", err)
  }
  + if head.BaseFee == nil {
  + return nil, nil, fmt.Errorf("failed to get L1 basefee in block %d for fee cap", head.Number)
  + }
  gasFeeCap = txmgr.CalcGasFeeCap(head.BaseFee, gasTipCap)
  return gasTipCap, gasFeeCap, nil
  