Fix filtering logic for networks with legacy transactions (#199)

Author: hazim-j

pkg/modules/gasprice/filter.go

@@ -3,6 +3,7 @@ package gasprice
 import (
 	"math/big"
 
+	"github.com/ethereum/go-ethereum/common"
 	"github.com/stackup-wallet/stackup-bundler/pkg/modules"
 	"github.com/stackup-wallet/stackup-bundler/pkg/userop"
 )
@@ -13,7 +14,7 @@ func FilterUnderpriced() modules.BatchHandlerFunc {
 	return func(ctx *modules.BatchHandlerCtx) error {
 		b := []*userop.UserOperation{}
 		for _, op := range ctx.Batch {
-			if ctx.BaseFee != nil && ctx.Tip != nil {
+			if ctx.BaseFee != nil && ctx.BaseFee.Cmp(common.Big0) != 0 && ctx.Tip != nil {
 				gp := big.NewInt(0).Add(ctx.BaseFee, ctx.Tip)
 				if op.GetDynamicGasPrice(ctx.BaseFee).Cmp(gp) >= 0 {
 					b = append(b, op)