diff --git a/umap/static/umap/js/modules/sync/engine.js b/umap/static/umap/js/modules/sync/engine.js
index 186615b6..2af5dfb6 100644
--- a/umap/static/umap/js/modules/sync/engine.js
+++ b/umap/static/umap/js/modules/sync/engine.js
@@ -3,15 +3,12 @@ import { MapUpdater, DataLayerUpdater, FeatureUpdater } from './updaters.js'
 
 export class SyncEngine {
   constructor(map) {
-    this.map = map
-    this.dispatcher = new MessagesDispatcher(this.map)
-    this._initialize()
-  }
-  _initialize() {
+    this.updaters = {
+      map: new MapUpdater(map),
+      feature: new FeatureUpdater(map),
+      datalayer: new DataLayerUpdater(map),
+    }
     this.transport = undefined
-    const noop = () => {}
-    // by default, all operations do nothing, until the engine is started.
-    this.upsert = this.update = this.delete = noop
   }
 
   async authenticate(tokenURI, webSocketURI, server) {
@@ -22,16 +19,47 @@ export class SyncEngine {
   }
 
   start(webSocketURI, authToken) {
-    this.transport = new WebSocketTransport(webSocketURI, authToken, this.dispatcher)
-    this.sender = new MessagesSender(this.transport)
-    this.upsert = this.sender.upsert.bind(this.sender)
-    this.update = this.sender.update.bind(this.sender)
-    this.delete = this.sender.delete.bind(this.sender)
+    this.transport = new WebSocketTransport(webSocketURI, authToken, this)
   }
 
   stop() {
     if (this.transport) this.transport.close()
-    this._initialize()
+    this.transport = undefined
+  }
+
+  _getUpdater(subject, metadata) {
+    if (Object.keys(this.updaters).includes(subject)) {
+      return this.updaters[subject]
+    }
+    throw new Error(`Unknown updater ${subject}, ${metadata}`)
+  }
+
+  // This method is called by the transport layer on new messages
+  receive({ kind, ...payload }) {
+    if (kind == 'operation') {
+      let updater = this._getUpdater(payload.subject, payload.metadata)
+      updater.applyMessage(payload)
+    } else {
+      throw new Error(`Unknown dispatch kind: ${kind}`)
+    }
+  }
+
+  _send(message) {
+    if (this.transport) {
+      this.transport.send('operation', message)
+    }
+  }
+
+  upsert(subject, metadata, value) {
+    this._send({ verb: 'upsert', subject, metadata, value })
+  }
+
+  update(subject, metadata, key, value) {
+    this._send({ verb: 'update', subject, metadata, key, value })
+  }
+
+  delete(subject, metadata, key) {
+    this._send({ verb: 'delete', subject, metadata, key })
   }
 
   /**
@@ -63,60 +91,3 @@ export class SyncEngine {
     return new Proxy(this, handler)
   }
 }
-
-export class MessagesDispatcher {
-  constructor(map) {
-    this.map = map
-    this.updaters = {
-      map: new MapUpdater(this.map),
-      feature: new FeatureUpdater(this.map),
-      datalayer: new DataLayerUpdater(this.map),
-    }
-  }
-
-  getUpdater(subject, metadata) {
-    if (Object.keys(this.updaters).includes(subject)) {
-      return this.updaters[subject]
-    }
-    throw new Error(`Unknown updater ${subject}, ${metadata}`)
-  }
-
-  dispatch({ kind, ...payload }) {
-    if (kind == 'operation') {
-      let updater = this.getUpdater(payload.subject, payload.metadata)
-      updater.applyMessage(payload)
-    } else {
-      throw new Error(`Unknown dispatch kind: ${kind}`)
-    }
-  }
-}
-
-/**
- * Send messages to other connected peers, using the specified transport.
- *
- * - `subject` is the type of object this is referering to (map, feature, layer)
- * - `metadata` contains information about the object we're refering to (id, layerId for instance)
- * - `key` and
- * - `value` are the keys and values that are being modified.
- */
-export class MessagesSender {
-  constructor(transport) {
-    this._transport = transport
-  }
-
-  send(message) {
-    this._transport.send('operation', message)
-  }
-
-  upsert(subject, metadata, value) {
-    this.send({ verb: 'upsert', subject, metadata, value })
-  }
-
-  update(subject, metadata, key, value) {
-    this.send({ verb: 'update', subject, metadata, key, value })
-  }
-
-  delete(subject, metadata, key) {
-    this.send({ verb: 'delete', subject, metadata, key })
-  }
-}
diff --git a/umap/static/umap/js/modules/sync/updaters.js b/umap/static/umap/js/modules/sync/updaters.js
index 9d83e001..a64e351d 100644
--- a/umap/static/umap/js/modules/sync/updaters.js
+++ b/umap/static/umap/js/modules/sync/updaters.js
@@ -15,7 +15,7 @@ class BaseUpdater {
     // Reduce the current list of attributes,
     // to find the object to set the property onto
     const objectToSet = parts.reduce((currentObj, part) => {
-      if (part in currentObj) return currentObj[part]
+      if (currentObj !== undefined && part in currentObj) return currentObj[part]
     }, obj)
 
     // In case the given path doesn't exist, stop here
diff --git a/umap/static/umap/js/modules/sync/websocket.js b/umap/static/umap/js/modules/sync/websocket.js
index e575bed6..45854dc1 100644
--- a/umap/static/umap/js/modules/sync/websocket.js
+++ b/umap/static/umap/js/modules/sync/websocket.js
@@ -9,7 +9,7 @@ export class WebSocketTransport {
   }
 
   onMessage(wsMessage) {
-    this.receiver.dispatch(JSON.parse(wsMessage.data))
+    this.receiver.receive(JSON.parse(wsMessage.data))
   }
 
   send(kind, payload) {
diff --git a/umap/static/umap/unittests/sync.js b/umap/static/umap/unittests/sync.js
index a7eb464b..e20a5153 100644
--- a/umap/static/umap/unittests/sync.js
+++ b/umap/static/umap/unittests/sync.js
@@ -5,7 +5,7 @@ import pkg from 'chai'
 const { expect } = pkg
 
 import { MapUpdater } from '../js/modules/sync/updaters.js'
-import { MessagesDispatcher, SyncEngine } from '../js/modules/sync/engine.js'
+import { SyncEngine } from '../js/modules/sync/engine.js'
 
 describe('SyncEngine', () => {
   it('should initialize methods even before start', function () {
@@ -16,35 +16,33 @@ describe('SyncEngine', () => {
   })
 })
 
-describe('MessageDispatcher', () => {
-  describe('#dispatch', function () {
-    it('should raise an error on unknown updater', function () {
-      const dispatcher = new MessagesDispatcher({})
-      expect(() => {
-        dispatcher.dispatch({
-          kind: 'operation',
-          subject: 'unknown',
-          metadata: {},
-        })
-      }).to.throw(Error)
-    })
-    it('should produce an error on malformated messages', function () {
-      const dispatcher = new MessagesDispatcher({})
-      expect(() => {
-        dispatcher.dispatch({
-          yeah: 'yeah',
-          payload: { foo: 'bar' },
-        })
-      }).to.throw(Error)
-    })
-    it('should raise an unknown operations', function () {
-      const dispatcher = new MessagesDispatcher({})
-      expect(() => {
-        dispatcher.dispatch({
-          kind: 'something-else',
-        })
-      }).to.throw(Error)
-    })
+describe('#dispatch', function () {
+  it('should raise an error on unknown updater', function () {
+    const dispatcher = new SyncEngine({})
+    expect(() => {
+      dispatcher.dispatch({
+        kind: 'operation',
+        subject: 'unknown',
+        metadata: {},
+      })
+    }).to.throw(Error)
+  })
+  it('should produce an error on malformated messages', function () {
+    const dispatcher = new SyncEngine({})
+    expect(() => {
+      dispatcher.dispatch({
+        yeah: 'yeah',
+        payload: { foo: 'bar' },
+      })
+    }).to.throw(Error)
+  })
+  it('should raise an unknown operations', function () {
+    const dispatcher = new SyncEngine({})
+    expect(() => {
+      dispatcher.dispatch({
+        kind: 'something-else',
+      })
+    }).to.throw(Error)
   })
 })