add null check for syncState

[dennis84]

Fix:

Uncaught TypeError: Cannot read properties of undefined (reading 'binding')

when removing the plugins from prosemirror state. It seems that an awareness event from yCursorPlugin is received and processed after the plugins are destroyed.

To reproduce:

diff --git a/demo/prosemirror.js b/demo/prosemirror.js
index a1cc530..7712a19 100644
--- a/demo/prosemirror.js
+++ b/demo/prosemirror.js
@@ -18,21 +18,21 @@ window.addEventListener('load', () => {
   editor.setAttribute('id', 'editor')
   const editorContainer = document.createElement('div')
   editorContainer.insertBefore(editor, null)
-  const prosemirrorView = new EditorView(editor, {
-    state: EditorState.create({
-      schema,
-      plugins: [
-        ySyncPlugin(type),
-        yCursorPlugin(provider.awareness),
-        yUndoPlugin(),
-        keymap({
-          'Mod-z': undo,
-          'Mod-y': redo,
-          'Mod-Shift-z': redo
-        })
-      ].concat(exampleSetup({ schema }))
-    })
+  let editorState = EditorState.create({
+    schema,
+    plugins: [
+      ySyncPlugin(type),
+      yCursorPlugin(provider.awareness),
+      yUndoPlugin(),
+      keymap({
+        'Mod-z': undo,
+        'Mod-y': redo,
+        'Mod-Shift-z': redo
+      })
+    ].concat(exampleSetup({ schema }))
   })
+
+  const prosemirrorView = new EditorView(editor, {state: editorState})
   document.body.insertBefore(editorContainer, null)

   const connectBtn = /** @type {HTMLElement} */ (document.getElementById('y-connect-btn'))
@@ -40,6 +40,8 @@ window.addEventListener('load', () => {
     if (provider.shouldConnect) {
       provider.disconnect()
       connectBtn.textContent = 'Connect'
+      editorState = editorState.reconfigure({schema, plugins: exampleSetup({ schema })})
+      prosemirrorView.updateState(editorState)
     } else {
       provider.connect()
       connectBtn.textContent = 'Disconnect'

[dmonad]

Thank you!