title: Build compile errors in RxRealm.swift after RxRealm pod update: Type 'List<Element>' does not conform to protocol 'NotificationEmitter'
body: <p>Here's the top portion of the file RxRealm.swift. (nowhere else in the file are there compile errors nor the &quot;observe&quot; func.</p>
  <pre><code>//
  //  RxRealm extensions
  //
  //  Copyright (c) 2016 RxSwiftCommunity. All rights reserved.
  //  Check the LICENSE file for details
  //  Created by Marin Todorov
  //
  
  import Foundation
  import RealmSwift
  import RxSwift
  
  public enum RxRealmError: Error {
    case objectDeleted
    case unknown
  }
  
  // MARK: Realm Collections type extensions
  
  /**
   `NotificationEmitter` is a protocol to allow for Realm's collections to be handled in a generic way.
  
   All collections already include a `addNotificationBlock(_:)` method - making them conform to `NotificationEmitter` just makes it easier to add Rx methods to them.
  
   The methods of essence in this protocol are `asObservable(...)`, which allow for observing for changes on Realm's collections.
   */
  public protocol NotificationEmitter {
    associatedtype ElementType: RealmCollectionValue
  
    /**
     Returns a `NotificationToken`, which while retained enables change notifications for the current collection.
  
     - returns: `NotificationToken` - retain this value to keep notifications being emitted for the current collection.
     */
    func observe(on queue: DispatchQueue?, _ block: @escaping (RealmCollectionChange&lt;Self&gt;) -&gt; Void) -&gt; NotificationToken
  
    func toArray() -&gt; [ElementType]
  
    func toAnyCollection() -&gt; AnyRealmCollection&lt;ElementType&gt;
  }
  
  extension List: NotificationEmitter {
    public func toAnyCollection() -&gt; AnyRealmCollection&lt;Element&gt; {
      return AnyRealmCollection&lt;Element&gt;(self)
    }
  
    public typealias ElementType = Element
    public func toArray() -&gt; [Element] {
      return Array(self)
    }
  }
  
  extension AnyRealmCollection: NotificationEmitter {
    public func toAnyCollection() -&gt; AnyRealmCollection&lt;Element&gt; {
      return AnyRealmCollection&lt;ElementType&gt;(self)
    }
  
    public typealias ElementType = Element
    public func toArray() -&gt; [Element] {
      return Array(self)
    }
  }
  
  extension Results: NotificationEmitter {
    public func toAnyCollection() -&gt; AnyRealmCollection&lt;Element&gt; {
      return AnyRealmCollection&lt;ElementType&gt;(self)
    }
  
    public typealias ElementType = Element
    public func toArray() -&gt; [Element] {
      return Array(self)
    }
  }
  
  extension LinkingObjects: NotificationEmitter {
    public func toAnyCollection() -&gt; AnyRealmCollection&lt;Element&gt; {
      return AnyRealmCollection&lt;ElementType&gt;(self)
    }
  
    public typealias ElementType = Element
    public func toArray() -&gt; [Element] {
      return Array(self)
    }
  }
  </code></pre>
  <p>I've tried adding the protocol stubs as suggested but I don't know what goes inside the added observe function.</p>
  <pre><code>public func observe(on queue: DispatchQueue?, _ block: @escaping (RealmCollectionChange&lt;List&lt;Element&gt;&gt;) -&gt; Void) -&gt; NotificationToken {
          // what goes here? 
      }
  </code></pre>
  <p>I've tried leaving the function blank but it spits out another error: &quot;Missing return in a function expected to return 'NotificationToken' (aka 'RLMNotificationToken')&quot;</p>
  <p>If I put in a return function I have no idea what to put in there. Obv it's the NotificiationToken type, but now I'm lost.</p>
  <p>This is really above my head, but there's nothing about it on Cocoapods <a href="https://cocoapods.org/pods/RxRealm" rel="nofollow noreferrer">https://cocoapods.org/pods/RxRealm</a></p>
  <p>Any ideas how to fix this?</p>