Handle unset base fee

Not necessary for celo, but for pre EIP-1559 tests.

core/state_transition.go

@@ -254,27 +254,22 @@ type StateTransition struct {
 	evm          *vm.EVM
 
 	// Celo additions
-	gasPriceMinimum *big.Int
-	backend         *CeloBackend
+	backend *CeloBackend
 }
 
 // NewStateTransition initialises and returns a new state transition object.
 func NewStateTransition(evm *vm.EVM, msg *Message, gp *GasPool) *StateTransition {
-	gasPriceMinimum := evm.Context.BaseFee
-	// TODO(pl): Convert base fee into fee currency of necessary
-
 	backend := &CeloBackend{
 		chainConfig: nil,
 		state:       nil,
 	}
 
 	return &StateTransition{
-		gp:              gp,
-		evm:             evm,
-		msg:             msg,
-		state:           evm.StateDB,
-		gasPriceMinimum: gasPriceMinimum,
-		backend:         backend,
+		gp:      gp,
+		evm:     evm,
+		msg:     msg,
+		state:   evm.StateDB,
+		backend: backend,
 	}
 }
 
@@ -688,7 +683,7 @@ func (st *StateTransition) distributeTxFees() error {
 	from := st.msg.From
 
 	// Divide the transaction into a base (the minimum transaction fee) and tip (any extra, or min(max tip, feecap - GPM) if espresso).
-	baseTxFee := new(big.Int).Mul(gasUsed, st.gasPriceMinimum)
+	baseTxFee := new(big.Int).Mul(gasUsed, st.calculateGasPriceMinimum())
 	// No need to do effectiveTip calculation, because st.gasPrice == effectiveGasPrice, and effectiveTip = effectiveGasPrice - baseTxFee
 	tipTxFee := new(big.Int).Sub(totalTxFee, baseTxFee)
 
@@ -710,3 +705,13 @@ func (st *StateTransition) distributeTxFees() error {
 	}
 	return nil
 }
+
+func (st *StateTransition) calculateGasPriceMinimum() *big.Int {
+	gasPriceMinimum := st.evm.Context.BaseFee
+	if gasPriceMinimum == nil {
+		gasPriceMinimum = big.NewInt(0)
+	}
+	// TODO(pl): Convert base fee into fee currency of necessary
+
+	return gasPriceMinimum
+}