Fix other .equals(null) (#541)

src/structures/GroupDMChannel.js

@@ -55,6 +55,7 @@ class GroupDMChannel extends Channel {
 
   equals(other) {
     const base = (
+      other &&
       this.id === other.id &&
       this.name === other.name &&
       this.icon === other.icon &&

src/structures/Guild.js

@@ -166,6 +166,7 @@ class Guild {
    */
   equals(data) {
     let base =
+      data &&
       this.id === data.id &&
       this.available === !data.unavailable &&
       this.splash === data.splash &&

src/structures/GuildChannel.js

@@ -67,6 +67,7 @@ class GuildChannel extends Channel {
    */
   equals(other) {
     let base = (
+      other &&
       this.type === other.type &&
       this.topic === other.topic &&
       this.position === other.position &&

src/structures/Role.js

@@ -22,6 +22,7 @@ class Role {
 
   equals(role) {
     return (
+      role &&
       this.id === role.id &&
       this.name === role.name &&
       this.color === role.color &&