diff --git a/client/lib/patch-db.ts b/client/lib/patch-db.ts
index de96130..58a1a13 100644
--- a/client/lib/patch-db.ts
+++ b/client/lib/patch-db.ts
@@ -2,9 +2,9 @@ import { merge, Observable, of } from 'rxjs'
 import { concatMap, finalize, tap } from 'rxjs/operators'
 import { Source } from './source/source'
 import { Store } from './store'
-import { DBCache, HashMap, Http } from './types'
+import { DBCache, Http } from './types'
 
-export class PatchDB<T extends HashMap> {
+export class PatchDB<T> {
   store: Store<T>
 
   constructor (
diff --git a/client/lib/source/source.ts b/client/lib/source/source.ts
index 300ad0a..45cf1b8 100644
--- a/client/lib/source/source.ts
+++ b/client/lib/source/source.ts
@@ -1,7 +1,7 @@
 import { Observable } from 'rxjs'
 import { Store } from '../store'
-import { HashMap, Update } from '../types'
+import { Update } from '../types'
 
-export interface Source<T extends HashMap> {
+export interface Source<T> {
   watch$ (store?: Store<T>): Observable<Update<T>>
 }
diff --git a/client/lib/store.ts b/client/lib/store.ts
index 7035244..abdf608 100644
--- a/client/lib/store.ts
+++ b/client/lib/store.ts
@@ -1,4 +1,4 @@
-import { DBCache, Dump, HashMap, Http, Revision, Update } from './types'
+import { DBCache, Dump, Http, Revision, Update } from './types'
 import { BehaviorSubject, Observable } from 'rxjs'
 import { applyOperation, getValueByPointer, Operation } from './json-patch-lib'
 import BTree from 'sorted-btree'
@@ -8,7 +8,7 @@ export interface StashEntry {
   undo: Operation[]
 }
 
-export class Store<T extends HashMap> {
+export class Store<T extends { [key: string]: any }> {
   cache: DBCache<T>
   sequence$: BehaviorSubject<number>
   private watchedNodes: { [path: string]: BehaviorSubject<any> } = { }
@@ -66,9 +66,13 @@ export class Store<T extends HashMap> {
   }
 
   private handleDump (dump: Dump<T>): void {
-    Object.keys(this.cache.data).forEach(key => delete this.cache.data[key])
-    Object.assign(this.cache.data, dump)
-    this.cache.data = dump.value
+    Object.keys(this.cache.data).forEach(key => {
+      if (dump.value[key] !== undefined) {
+        (this.cache.data as any)[key] = dump.value[key]
+      } else {
+        delete this.cache.data[key]
+      }
+    })
     this.stash.deleteRange(this.cache.sequence, dump.id, false)
     this.updateWatchedNodes('')
     this.updateSequence(dump.id)
diff --git a/client/lib/types.ts b/client/lib/types.ts
index ae683a0..278aaa9 100644
--- a/client/lib/types.ts
+++ b/client/lib/types.ts
@@ -3,9 +3,9 @@ import { Operation } from './json-patch-lib'
 // revise a collection of nodes.
 export type Revision = { id: number, patch: Operation[], expireId: string | null }
 // dump/replace the entire store with T
-export type Dump<T extends HashMap> = { id: number, value: T, expireId: string | null }
+export type Dump<T> = { id: number, value: T, expireId: string | null }
 
-export type Update<T extends HashMap> = Revision | Dump<T>
+export type Update<T> = Revision | Dump<T>
 
 export enum PatchOp {
   ADD = 'add',
@@ -13,20 +13,17 @@ export enum PatchOp {
   REPLACE = 'replace',
 }
 
-export interface Http<T extends HashMap> {
+export interface Http<T> {
   getRevisions (since: number): Promise<Revision[] | Dump<T>>
   getDump (): Promise<Dump<T>>
 }
 
-export interface Bootstrapper<T extends HashMap> {
+export interface Bootstrapper<T> {
   init (): Promise<DBCache<T>>
   update (cache: DBCache<T>): Promise<void>
 }
 
-export interface DBCache<T extends HashMap>{
+export interface DBCache<T extends { [key: string]: any }>{
   sequence: number,
   data: T
 }
-
-export type HashMap = { [type: string]: any }
-