fix relativePosition if startof is a root type

src/Type/YMap.js

@@ -36,7 +36,13 @@ export default class YMap extends Type {
     return map
   }
   keys () {
-    return Array.from(this._map.keys()).filter(x => !x._deleted)
+    let keys = []
+    for (let [key, value] of this._map) {
+      if (!value._deleted) {
+        keys.push(key)
+      }
+    }
+    return keys
   }
   delete (key) {
     this._transact((y) => {

src/Util/relativePosition.js

@@ -1,8 +1,9 @@
-import ID from './ID'
+import ID from './ID.js'
+import RootID from './RootID.js'
 
 export function getRelativePosition (type, offset) {
   if (offset === 0) {
-    return ['startof', type._id.user, type._id.clock]
+    return ['startof', type._id.user, type._id.clock || null, type._id.type || null]
   } else {
     let t = type._start
     while (t !== null) {
@@ -23,8 +24,14 @@ export function getRelativePosition (type, offset) {
 
 export function fromRelativePosition (y, rpos) {
   if (rpos[0] === 'startof') {
+    let id
+    if (rpos[3] === null) {
+      id = new ID(rpos[1], rpos[2])
+    } else {
+      id = new RootID(rpos[1], rpos[3])
+    }
     return {
-      type: y.os.get(new ID(rpos[1], rpos[2])),
+      type: y.os.get(id),
       offset: 0
     }
   } else {