Fix error when persisting actors w/o display name

lib/entity/Actor.ts

@@ -11,17 +11,17 @@ export default class Actor {
 	@Column({ type: "json" })
 	actorObject: ActorObject;
 
-	@Column()
+	@Column({ default: false })
 	isFollower: boolean;
 
-	@Column()
-	displayName: string;
+	@Column({ nullable: true })
+	displayName: string | null;
 	
 	@Column()
 	inbox: string;
 
-	@Column()
-	iconURL: string;
+	@Column({ nullable: true })
+	iconURL: string | null;
 
 	@Column({ nullable: true })
 	publicKeyPem: string | null;