diff --git a/api/channel.go b/api/channel.go
index 713f1a3..4d8f463 100644
--- a/api/channel.go
+++ b/api/channel.go
@@ -46,31 +46,24 @@ func (c *Client) CreateChannel(
 	)
 }
 
-func (c *Client) MoveChannel(
-	guildID, channelID discord.Snowflake, position int) error {
-
-	var param struct {
-		ID  discord.Snowflake `json:"id"`
-		Pos int               `json:"position"`
-	}
-
-	param.ID = channelID
-	param.Pos = position
+type MoveChannelData struct {
+	ID       discord.Snowflake `json:"id"`
+	Position json.OptionInt    `json:"position,omitempty"`
+}
 
+// MoveChannel modifies the position of channels in the guild. Requires
+// MANAGE_CHANNELS.
+func (c *Client) MoveChannel(guildID discord.Snowflake, datum []MoveChannelData) error {
 	return c.FastRequest(
 		"PATCH",
 		EndpointGuilds+guildID.String()+"/channels",
-		httputil.WithJSONBody(c, param),
+		httputil.WithJSONBody(c, datum),
 	)
 }
 
-func (c *Client) Channel(
-	channelID discord.Snowflake) (*discord.Channel, error) {
-
+func (c *Client) Channel(channelID discord.Snowflake) (*discord.Channel, error) {
 	var channel *discord.Channel
-
-	return channel,
-		c.RequestJSON(&channel, "GET", EndpointChannels+channelID.String())
+	return channel, c.RequestJSON(&channel, "GET", EndpointChannels+channelID.String())
 }
 
 type ModifyChannelData struct {
@@ -111,45 +104,36 @@ func (c *Client) DeleteChannel(channelID discord.Snowflake) error {
 func (c *Client) EditChannelPermission(
 	channelID discord.Snowflake, overwrite discord.Overwrite) error {
 
-	url := EndpointChannels + channelID.String() + "/permissions/" +
-		overwrite.ID.String()
+	url := EndpointChannels + channelID.String() + "/permissions/" + overwrite.ID.String()
 	overwrite.ID = 0
 
 	return c.FastRequest("PUT", url, httputil.WithJSONBody(c, overwrite))
 }
 
-func (c *Client) DeleteChannelPermission(
-	channelID, overwriteID discord.Snowflake) error {
-
-	return c.FastRequest("DELETE", EndpointChannels+channelID.String()+
-		"/permissions/"+overwriteID.String())
+func (c *Client) DeleteChannelPermission(channelID, overwriteID discord.Snowflake) error {
+	return c.FastRequest("DELETE",
+		EndpointChannels+channelID.String()+"/permissions/"+overwriteID.String())
 }
 
 // Typing posts a typing indicator to the channel. Undocumented, but the client
 // usually clears the typing indicator after 8-10 seconds (or after a message).
 func (c *Client) Typing(channelID discord.Snowflake) error {
-	return c.FastRequest("POST",
-		EndpointChannels+channelID.String()+"/typing")
+	return c.FastRequest("POST", EndpointChannels+channelID.String()+"/typing")
 }
 
-func (c *Client) PinnedMessages(
-	channelID discord.Snowflake) ([]discord.Message, error) {
-
+func (c *Client) PinnedMessages(channelID discord.Snowflake) ([]discord.Message, error) {
 	var pinned []discord.Message
-	return pinned, c.RequestJSON(&pinned, "GET",
-		EndpointChannels+channelID.String()+"/pins")
+	return pinned, c.RequestJSON(&pinned, "GET", EndpointChannels+channelID.String()+"/pins")
 }
 
 // PinMessage pins a message, which requires MANAGE_MESSAGES/
 func (c *Client) PinMessage(channelID, messageID discord.Snowflake) error {
-	return c.FastRequest("PUT",
-		EndpointChannels+channelID.String()+"/pins/"+messageID.String())
+	return c.FastRequest("PUT", EndpointChannels+channelID.String()+"/pins/"+messageID.String())
 }
 
 // UnpinMessage also requires MANAGE_MESSAGES.
 func (c *Client) UnpinMessage(channelID, messageID discord.Snowflake) error {
-	return c.FastRequest("DELETE",
-		EndpointChannels+channelID.String()+"/pins/"+messageID.String())
+	return c.FastRequest("DELETE", EndpointChannels+channelID.String()+"/pins/"+messageID.String())
 }
 
 // AddRecipient adds a user to a group direct message. As accessToken is needed,
@@ -179,13 +163,14 @@ func (c *Client) RemoveRecipient(channelID, userID discord.Snowflake) error {
 		EndpointChannels+channelID.String()+"/recipients/"+userID.String())
 }
 
-// ACk is the read state of a channel. This is undocumented.
+// Ack is the read state of a channel. This is undocumented.
 type Ack struct {
 	Token string `json:"token"`
 }
 
 // Ack marks the read state of a channel. This is undocumented. The method will
-// write to the ack variable passed in.
+// write to the ack variable passed in. If this method is called asynchronously,
+// then ack should be mutex guarded.
 func (c *Client) Ack(channelID, messageID discord.Snowflake, ack *Ack) error {
 	return c.RequestJSON(
 		ack, "POST",
diff --git a/api/guild.go b/api/guild.go
index e902468..b57def6 100644
--- a/api/guild.go
+++ b/api/guild.go
@@ -5,6 +5,7 @@ import (
 
 	"github.com/diamondburned/arikawa/discord" // for clarity
 	"github.com/diamondburned/arikawa/utils/httputil"
+	"github.com/diamondburned/arikawa/utils/json"
 )
 
 var EndpointGuilds = Endpoint + "guilds/"
@@ -118,9 +119,8 @@ func (c *Client) LeaveGuild(guildID discord.Snowflake) error {
 
 // https://discordapp.com/developers/docs/resources/guild#modify-guild-json-params
 type ModifyGuildData struct {
-	Name   string `json:"name,omitempty"`
-	Region string `json:"region,omitempty"`
-	Icon   Image  `json:"image,omitempty"`
+	Name   string            `json:"name,omitempty"`
+	Region json.OptionString `json:"region,omitempty"`
 
 	// package d is just package discord
 	Verification   *discord.Verification   `json:"verification_level,omitempty"`
@@ -130,12 +130,17 @@ type ModifyGuildData struct {
 	AFKChannelID *discord.Snowflake `json:"afk_channel_id,string,omitempty"`
 	AFKTimeout   *discord.Seconds   `json:"afk_timeout,omitempty"`
 
-	OwnerID discord.Snowflake `json:"owner_id,string,omitempty"`
+	OwnerID discord.Snowflake `json:"owner_id,omitempty"`
 
-	Splash Image `json:"splash,omitempty"`
-	Banner Image `json:"banner,omitempty"`
+	Icon   *Image `json:"icon,omitempty"`
+	Splash *Image `json:"splash,omitempty"`
+	Banner *Image `json:"banner,omitempty"`
 
-	SystemChannelID discord.Snowflake `json:"system_channel_id,string,omitempty"`
+	SystemChannelID        *discord.Snowflake `json:"system_channel_id,omitempty"`
+	RulesChannelID         *discord.Snowflake `json:"rules_channel_id,omitempty"`
+	PublicUpdatesChannelID *discord.Snowflake `json:"public_updates_channel_id,omitempty"`
+
+	PreferredLocale json.OptionString `json:"preferred_locale,omitempty"`
 }
 
 func (c *Client) ModifyGuild(
diff --git a/api/image.go b/api/image.go
index 85a1b5a..c40a928 100644
--- a/api/image.go
+++ b/api/image.go
@@ -3,10 +3,10 @@ package api
 import (
 	"bytes"
 	"encoding/base64"
-	"encoding/json"
 	"fmt"
 	"net/http"
 
+	"github.com/diamondburned/arikawa/utils/json"
 	"github.com/pkg/errors"
 )
 
@@ -32,9 +32,6 @@ type Image struct {
 
 	// Just raw content of the file.
 	Content []byte
-
-	// Utility fields, not used for encoding
-	MaxSize int // bytes
 }
 
 func DecodeImage(data []byte) (*Image, error) {
@@ -61,9 +58,9 @@ func DecodeImage(data []byte) (*Image, error) {
 	return &img, nil
 }
 
-func (i Image) Validate() error {
-	if i.MaxSize > 0 && len(i.Content) > i.MaxSize {
-		return ErrImageTooLarge{len(i.Content), i.MaxSize}
+func (i Image) Validate(maxSize int) error {
+	if maxSize > 0 && len(i.Content) > maxSize {
+		return ErrImageTooLarge{len(i.Content), maxSize}
 	}
 
 	switch i.ContentType {
@@ -83,7 +80,7 @@ func (i Image) Encode() ([]byte, error) {
 		i.ContentType = http.DetectContentType(i.Content[:max])
 	}
 
-	if err := i.Validate(); err != nil {
+	if err := i.Validate(0); err != nil {
 		return nil, err
 	}
 
@@ -118,8 +115,9 @@ func (i *Image) UnmarshalJSON(v []byte) error {
 	// Trim string
 	v = bytes.Trim(v, `"`)
 
+	// Accept a nil image.
 	if string(v) == "null" {
-		return ErrNoImage
+		return nil
 	}
 
 	img, err := DecodeImage(v)
diff --git a/api/member.go b/api/member.go
index 4ec4401..42be17e 100644
--- a/api/member.go
+++ b/api/member.go
@@ -3,6 +3,7 @@ package api
 import (
 	"github.com/diamondburned/arikawa/discord"
 	"github.com/diamondburned/arikawa/utils/httputil"
+	"github.com/diamondburned/arikawa/utils/json"
 )
 
 func (c *Client) Member(
@@ -81,14 +82,14 @@ func (c *Client) MembersAfter(
 
 // AnyMemberData, all fields are optional.
 type AnyMemberData struct {
-	Nick string `json:"nick,omitempty"`
-	Mute bool   `json:"mute,omitempty"`
-	Deaf bool   `json:"deaf,omitempty"`
+	Nick json.OptionString `json:"nick,omitempty"`
+	Mute json.OptionBool   `json:"mute,omitempty"`
+	Deaf json.OptionBool   `json:"deaf,omitempty"`
 
-	Roles []discord.Snowflake `json:"roles,omitempty"`
+	Roles *[]discord.Snowflake `json:"roles,omitempty"`
 
 	// Only for ModifyMember, requires MOVE_MEMBER
-	VoiceChannel discord.Snowflake `json:"channel_id,omitempty"`
+	VoiceChannel *discord.Snowflake `json:"channel_id,omitempty"`
 }
 
 // AddMember requires access(Token).
@@ -96,8 +97,8 @@ func (c *Client) AddMember(
 	guildID, userID discord.Snowflake, token string,
 	data AnyMemberData) (*discord.Member, error) {
 
-	// VoiceChannel doesn't belong here
-	data.VoiceChannel = 0
+	// VoiceChannel doesn't belong here.
+	data.VoiceChannel = nil
 
 	var param struct {
 		Token string `json:"access_token"`
@@ -108,6 +109,7 @@ func (c *Client) AddMember(
 	param.AnyMemberData = data
 
 	var mem *discord.Member
+
 	return mem, c.RequestJSON(
 		&mem, "PUT",
 		EndpointGuilds+guildID.String()+"/members/"+userID.String(),
@@ -127,9 +129,7 @@ func (c *Client) ModifyMember(
 
 // PruneCount returns the number of members that would be removed in a prune
 // operation. Requires KICK_MEMBERS. Days must be 1 or more, default 7.
-func (c *Client) PruneCount(
-	guildID discord.Snowflake, days uint) (uint, error) {
-
+func (c *Client) PruneCount(guildID discord.Snowflake, days uint) (uint, error) {
 	if days == 0 {
 		days = 7
 	}
@@ -153,9 +153,7 @@ func (c *Client) PruneCount(
 
 // Prune returns the number of members that is removed. Requires KICK_MEMBERS.
 // Days must be 1 or more, default 7.
-func (c *Client) Prune(
-	guildID discord.Snowflake, days uint) (uint, error) {
-
+func (c *Client) Prune(guildID discord.Snowflake, days uint) (uint, error) {
 	if days == 0 {
 		days = 7
 	}
@@ -191,9 +189,7 @@ func (c *Client) Bans(guildID discord.Snowflake) ([]discord.Ban, error) {
 		EndpointGuilds+guildID.String()+"/bans")
 }
 
-func (c *Client) GetBan(
-	guildID, userID discord.Snowflake) (*discord.Ban, error) {
-
+func (c *Client) GetBan(guildID, userID discord.Snowflake) (*discord.Ban, error) {
 	var ban *discord.Ban
 	return ban, c.RequestJSON(&ban, "GET",
 		EndpointGuilds+guildID.String()+"/bans/"+userID.String())
@@ -201,9 +197,7 @@ func (c *Client) GetBan(
 
 // Ban requires the BAN_MEMBERS permission. Days is the days back for Discord
 // to delete the user's message, maximum 7 days.
-func (c *Client) Ban(
-	guildID, userID discord.Snowflake, days uint, reason string) error {
-
+func (c *Client) Ban(guildID, userID discord.Snowflake, days uint, reason string) error {
 	if days > 7 {
 		days = 7
 	}
@@ -223,8 +217,7 @@ func (c *Client) Ban(
 	)
 }
 
-// Unban also requires BAN_MEMBERS.
+// Unban requires BAN_MEMBERS.
 func (c *Client) Unban(guildID, userID discord.Snowflake) error {
-	return c.FastRequest("DELETE",
-		EndpointGuilds+guildID.String()+"/bans/"+userID.String())
+	return c.FastRequest("DELETE", EndpointGuilds+guildID.String()+"/bans/"+userID.String())
 }
diff --git a/utils/json/raw.go b/utils/json/raw.go
index 59385c3..b04114f 100644
--- a/utils/json/raw.go
+++ b/utils/json/raw.go
@@ -1,5 +1,13 @@
 package json
 
+type Marshaler interface {
+	MarshalJSON() ([]byte, error)
+}
+
+type Unmarshaler interface {
+	UnmarshalJSON([]byte) error
+}
+
 // Raw is a raw encoded JSON value. It implements Marshaler and Unmarshaler and
 // can be used to delay JSON decoding or precompute a JSON encoding. It's taken
 // from encoding/json.