fix: nil pointer dereferencing in writeArg (#3271)

* fixed bug with nil dereferencing in writeArg, added hset struct example, added tests

* removed password from example

* added omitempty

* reverted xxhash versioning

* reverted xxhash versioning

* removed password

* removed password

---------

Co-authored-by: Nedyalko Dyakov <nedyalko.dyakov@gmail.com>

example/hset-struct/main.go

@@ -0,0 +1,129 @@
+package main
+
+import (
+	"context"
+	"time"
+
+	"github.com/davecgh/go-spew/spew"
+
+	"github.com/redis/go-redis/v9"
+)
+
+type Model struct {
+	Str1    string     `redis:"str1"`
+	Str2    string     `redis:"str2"`
+	Str3    *string    `redis:"str3"`
+	Str4    *string    `redis:"str4"`
+	Bytes   []byte     `redis:"bytes"`
+	Int     int        `redis:"int"`
+	Int2    *int       `redis:"int2"`
+	Int3    *int       `redis:"int3"`
+	Bool    bool       `redis:"bool"`
+	Bool2   *bool      `redis:"bool2"`
+	Bool3   *bool      `redis:"bool3"`
+	Bool4   *bool      `redis:"bool4,omitempty"`
+	Time    time.Time  `redis:"time"`
+	Time2   *time.Time `redis:"time2"`
+	Time3   *time.Time `redis:"time3"`
+	Ignored struct{}   `redis:"-"`
+}
+
+func main() {
+	ctx := context.Background()
+
+	rdb := redis.NewClient(&redis.Options{
+		Addr: ":6379",
+	})
+
+	_ = rdb.FlushDB(ctx).Err()
+
+	t := time.Date(2025, 02, 8, 0, 0, 0, 0, time.UTC)
+
+	data := Model{
+		Str1:    "hello",
+		Str2:    "world",
+		Str3:    ToPtr("hello"),
+		Str4:    nil,
+		Bytes:   []byte("this is bytes !"),
+		Int:     123,
+		Int2:    ToPtr(0),
+		Int3:    nil,
+		Bool:    true,
+		Bool2:   ToPtr(false),
+		Bool3:   nil,
+		Time:    t,
+		Time2:   ToPtr(t),
+		Time3:   nil,
+		Ignored: struct{}{},
+	}
+
+	// Set some fields.
+	if _, err := rdb.Pipelined(ctx, func(rdb redis.Pipeliner) error {
+		rdb.HMSet(ctx, "key", data)
+		return nil
+	}); err != nil {
+		panic(err)
+	}
+
+	var model1, model2 Model
+
+	// Scan all fields into the model.
+	if err := rdb.HGetAll(ctx, "key").Scan(&model1); err != nil {
+		panic(err)
+	}
+
+	// Or scan a subset of the fields.
+	if err := rdb.HMGet(ctx, "key", "str1", "int").Scan(&model2); err != nil {
+		panic(err)
+	}
+
+	spew.Dump(model1)
+	// Output:
+	// (main.Model) {
+	//  Str1: (string) (len=5) "hello",
+	//  Str2: (string) (len=5) "world",
+	//  Str3: (*string)(0xc000016970)((len=5) "hello"),
+	//  Str4: (*string)(0xc000016980)(""),
+	//  Bytes: ([]uint8) (len=15 cap=16) {
+	//   00000000  74 68 69 73 20 69 73 20  62 79 74 65 73 20 21     |this is bytes !|
+	//  },
+	//  Int: (int) 123,
+	//  Int2: (*int)(0xc000014568)(0),
+	//  Int3: (*int)(0xc000014560)(0),
+	//  Bool: (bool) true,
+	//  Bool2: (*bool)(0xc000014570)(false),
+	//  Bool3: (*bool)(0xc000014548)(false),
+	//  Bool4: (*bool)(<nil>),
+	//  Time: (time.Time) 2025-02-08 00:00:00 +0000 UTC,
+	//  Time2: (*time.Time)(0xc0000122a0)(2025-02-08 00:00:00 +0000 UTC),
+	//  Time3: (*time.Time)(0xc000012288)(0001-01-01 00:00:00 +0000 UTC),
+	//  Ignored: (struct {}) {
+	//  }
+	// }
+
+	spew.Dump(model2)
+	// Output:
+	// (main.Model) {
+	//  Str1: (string) (len=5) "hello",
+	//  Str2: (string) "",
+	//  Str3: (*string)(<nil>),
+	//  Str4: (*string)(<nil>),
+	//  Bytes: ([]uint8) <nil>,
+	//  Int: (int) 123,
+	//  Int2: (*int)(<nil>),
+	//  Int3: (*int)(<nil>),
+	//  Bool: (bool) false,
+	//  Bool2: (*bool)(<nil>),
+	//  Bool3: (*bool)(<nil>),
+	//  Bool4: (*bool)(<nil>),
+	//  Time: (time.Time) 0001-01-01 00:00:00 +0000 UTC,
+	//  Time2: (*time.Time)(<nil>),
+	//  Time3: (*time.Time)(<nil>),
+	//  Ignored: (struct {}) {
+	//  }
+	// }
+}
+
+func ToPtr[T any](v T) *T {
+	return &v
+}