fix: fix error is not nil if it is a nil pointer

Signed-off-by: Chen Su <ghosind@gmail.com>

Author: ghosind

all_test.go

@@ -11,6 +11,12 @@ import (
 	"github.com/ghosind/go-async"
 )
 
+type testError struct{}
+
+func (e *testError) Error() string {
+	return "test error"
+}
+
 func TestAllWithoutFuncs(t *testing.T) {
 	a := assert.New(t)
 
@@ -101,6 +107,18 @@ func TestAllWithTimeoutContext(t *testing.T) {
 	a.EqualNow(out, [][]any{{nil}, {nil}, nil, nil, nil})
 }
 
+func TestAllWithTestError(t *testing.T) {
+	a := assert.New(t)
+
+	_, err := async.All(func() error {
+		var e *testError
+		return e
+	}, func() *testError {
+		return nil
+	})
+	a.NilNow(err)
+}
+
 func BenchmarkAll(b *testing.B) {
 	tasks := make([]async.AsyncFn, 0, 1000)
 	for i := 0; i < 1000; i++ {

async.go

@@ -142,6 +142,10 @@ func invokeAsyncFn(fn AsyncFn, ctx context.Context, params []any) ([]any, error)
 			err = nil
 		} else {
 			err = out[numRet-1].Interface().(error)
+			// double check if the error is a custom error pointer
+			if err == nil || reflect.ValueOf(err).IsNil() {
+				err = nil
+			}
 		}
 	}
 	for i := 0; i < numRet; i++ {

async_test.go

@@ -230,5 +230,4 @@ func TestInvokeAsyncFnWithParams(t *testing.T) {
 	a.PanicOfNow(func() {
 		invokeAsyncFn(func(ctx context.Context, n int) {}, ctx, []any{"hello"})
 	}, ErrUnmatchedParam)
-
 }