Return error if the CCR was done to an empty contract (#227)

internal/ethapi/api.go

@@ -2031,6 +2031,16 @@ func runMEVM(ctx context.Context, b Backend, state *state.StateDB, header *types
 		return nil, result, nil, nil
 	}
 
+	if result.ReturnData == nil {
+		// If the CCR returns empty data, it might be because it was done with a non-existent
+		// contract. Validate if that is true (code == 0) and return error.
+		// Note that we cannot do this check before "ApplyMessage" because we might be
+		// discarding the execution of precompiles which do not have code.
+		if code := state.GetCode(*msg.To); len(code) == 0 {
+			return nil, nil, nil, fmt.Errorf("target contract does not exist")
+		}
+	}
+
 	if storageAccessTracer.hasStoredState {
 		return nil, nil, nil, fmt.Errorf("confidential request cannot modify state storage")
 	}

suave/e2e/workflow_test.go

@@ -1366,6 +1366,21 @@ func TestE2E_Precompile_RandomBytes(t *testing.T) {
 	require.Len(t, res[0], 64)
 }
 
+func TestE2E_EmptyAddress(t *testing.T) {
+	// it should not be possible to make a CCR to an empty address
+	fr := newFramework(t)
+	defer fr.Close()
+
+	clt := fr.NewSDKClient()
+
+	// 0xa contract does not exist
+	contractAddr := common.Address{0xa}
+	sourceContract := sdk.GetContract(contractAddr, exampleCallSourceContract.Abi, clt)
+
+	_, err := sourceContract.SendTransaction("consoleLog", []interface{}{}, nil)
+	require.Error(t, err)
+}
+
 type clientWrapper struct {
 	t *testing.T