refactor(hooks): reduce null types (#3111)

(cherry picked from commit 8b5d997322)

packages/hooks/src/use-block-suite-workspace-helper.ts

@@ -1,4 +1,3 @@
-import { assertExists } from '@blocksuite/global/utils';
 import type { Page, Workspace } from '@blocksuite/store';
 import { useMemo } from 'react';
 
@@ -6,7 +5,6 @@ export function useBlockSuiteWorkspaceHelper(blockSuiteWorkspace: Workspace) {
   return useMemo(
     () => ({
       createPage: (pageId?: string): Page => {
-        assertExists(blockSuiteWorkspace);
         return blockSuiteWorkspace.createPage({ id: pageId });
       },
     }),