fix marshaling of empty values

internal/ethapi/api.go

@@ -19,6 +19,7 @@ package ethapi
 import (
 	"context"
 	"encoding/hex"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"math/big"
@@ -1107,7 +1108,16 @@ type callResult struct {
 	Logs        []*types.Log   `json:"logs"`
 	Transfers   []transfer     `json:"transfers,omitempty"`
 	GasUsed     hexutil.Uint64 `json:"gasUsed"`
-	Error       string         `json:"error"`
+	Error       string         `json:"error,omitempty"`
+}
+
+func (r *callResult) MarshalJSON() ([]byte, error) {
+	type callResultAlias callResult
+	// Marshal logs to be an empty array instead of nil when empty
+	if r.Logs == nil {
+		r.Logs = []*types.Log{}
+	}
+	return json.Marshal((*callResultAlias)(r))
 }
 
 // Multicall executes series of transactions on top of a base state.

internal/ethapi/api_test.go

@@ -670,10 +670,12 @@ func TestMulticall(t *testing.T) {
 				res{
 					ReturnValue: "0x",
 					GasUsed:     "0x5208",
+					Logs:        []types.Log{},
 				},
 				res{
 					ReturnValue: "0x",
 					GasUsed:     "0x5208",
+					Logs:        []types.Log{},
 				},
 			}},
 		}, {
@@ -715,19 +717,23 @@ func TestMulticall(t *testing.T) {
 					res{
 						ReturnValue: "0x",
 						GasUsed:     "0x5208",
+						Logs:        []types.Log{},
 					},
 					res{
 						ReturnValue: "0x",
 						GasUsed:     "0x5208",
+						Logs:        []types.Log{},
 					},
 				}, {
 					res{
 						ReturnValue: "0x",
 						GasUsed:     "0x5208",
+						Logs:        []types.Log{},
 					},
 					res{
 						ReturnValue: "0x",
 						GasUsed:     "0x0",
+						Logs:        []types.Log{},
 						Error:       fmt.Sprintf("err: insufficient funds for gas * price + value: address %s have 0 want 1000 (supplied gas 9937000)", randomAccounts[3].addr.String()),
 					},
 				},
@@ -766,11 +772,13 @@ func TestMulticall(t *testing.T) {
 				res{
 					ReturnValue: "0x000000000000000000000000000000000000000000000000000000000000000b",
 					GasUsed:     "0xe891",
+					Logs:        []types.Log{},
 				},
 			}, {
 				res{
 					ReturnValue: "0x000000000000000000000000000000000000000000000000000000000000000c",
 					GasUsed:     "0xe891",
+					Logs:        []types.Log{},
 				},
 			}},
 		},
@@ -830,9 +838,11 @@ func TestMulticall(t *testing.T) {
 			want: [][]res{{{
 				ReturnValue: "0x",
 				GasUsed:     "0xaacc",
+				Logs:        []types.Log{},
 			}, {
 				ReturnValue: "0x0000000000000000000000000000000000000000000000000000000000000005",
 				GasUsed:     "0x5bb7",
+				Logs:        []types.Log{},
 			}}},
 		},
 		// Test logs output.
@@ -920,6 +930,7 @@ func TestMulticall(t *testing.T) {
 				// Caller is in this case the contract that invokes ecrecover.
 				ReturnValue: strings.ToLower(randomAccounts[2].addr.String()),
 				GasUsed:     "0x52f6",
+				Logs:        []types.Log{},
 			}}},
 		},
 		// Test ether transfers.
@@ -965,6 +976,7 @@ func TestMulticall(t *testing.T) {
 						Value: big.NewInt(100),
 					},
 				},
+				Logs: []types.Log{},
 			}}},
 		},
 	}