Support single request

Outputs type supports nil

README.md

@@ -19,6 +19,7 @@ go get github.com/forta-network/go-multicall
 
 (See other examples under the `examples` directory!)
 
+#### Multicall   
 ```go
 package main
 
@@ -91,3 +92,64 @@ func main() {
 	}
 }
 ```
+
+#### SingleCall   
+```go
+package main
+
+import (
+	"context"
+	"fmt"
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/forta-network/go-multicall"
+)
+
+const (
+	APIURL   = "https://cloudflare-eth.com"
+	ERC20ABI = `[
+		{
+			"constant":true,
+			"inputs":[
+					{
+						"name":"tokenOwner",
+						"type":"address"
+					}
+			],
+			"name":"balanceOf",
+			"outputs":[
+					{
+						"name":"balance",
+						"type":"uint256"
+					}
+			],
+			"payable":false,
+			"stateMutability":"view",
+			"type":"function"
+		}
+	]`
+)
+
+func main() {
+	caller, err := multicall.Dial(context.Background(), APIURL)
+	if err != nil {
+		panic(err)
+	}
+
+	contract, err := multicall.NewContract(ERC20ABI, "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48")
+	if err != nil {
+		panic(err)
+	}
+
+	single, err := caller.CallSingle(nil,
+		contract.NewCall(
+			nil,
+			"balanceOf",
+			common.HexToAddress("0xcEe284F754E854890e311e3280b767F80797180d"), // Arbitrum One gateway
+		).Name("Arbitrum One gateway balance"))
+	if err != nil {
+		return
+	}
+
+	fmt.Println(single.CallName, ":", single.Outputs, err)
+}
+```

call.go

@@ -2,7 +2,6 @@ package multicall
 
 import (
 	"bytes"
-	"errors"
 	"fmt"
 	"reflect"
 
@@ -80,15 +79,16 @@ func (call *Call) Unpack(b []byte) error {
 	if t.Kind() == reflect.Pointer {
 		t = t.Elem()
 	}
-	if t.Kind() != reflect.Struct {
-		return errors.New("outputs type is not a struct")
-	}
-
 	out, err := call.Contract.ABI.Unpack(call.Method, b)
 	if err != nil {
 		return fmt.Errorf("failed to unpack '%s' outputs: %v", call.Method, err)
 	}
 
+	if t.Kind() != reflect.Struct {
+		call.Outputs = out
+		return nil
+	}
+
 	fieldCount := t.NumField()
 	for i := 0; i < fieldCount; i++ {
 		field := t.Field(i)

caller.go

@@ -47,6 +47,19 @@ func Dial(ctx context.Context, rawUrl string, multicallAddr ...string) (*Caller,
 
 // Call makes multicalls.
 func (caller *Caller) Call(opts *bind.CallOpts, calls ...*Call) ([]*Call, error) {
+	return caller.calls(opts, calls...)
+}
+
+func (caller *Caller) CallSingle(opts *bind.CallOpts, call *Call) (*Call, error) {
+
+	calls, err := caller.calls(opts, call)
+	if err != nil {
+		return call, fmt.Errorf("CallSingle failed: %v", err)
+	}
+	return calls[0], nil
+}
+
+func (caller *Caller) calls(opts *bind.CallOpts, calls ...*Call) ([]*Call, error) {
 	var multiCalls []contract_multicall.Multicall3Call3
 
 	for i, call := range calls {
@@ -86,7 +99,7 @@ func (caller *Caller) CallChunked(opts *bind.CallOpts, chunkSize int, cooldown t
 			time.Sleep(cooldown)
 		}
 
-		chunk, err := caller.Call(opts, chunk...)
+		chunk, err := caller.calls(opts, chunk...)
 		if err != nil {
 			return calls, fmt.Errorf("call chunk [%d] failed: %v", i, err)
 		}