HarmonyOS 新API属性不能被定义为undefined吗？

import camera from '@ohos.multimedia.camera'; 
 
export default class CameraService { 
  private cameraMgr: camera.CameraManager = undefined; 
  private camerasArray: Array<camera.CameraDevice> = undefined; 
  private cameraInput: camera.CameraInput = undefined; 
  private previewOutput: camera.PreviewOutput = undefined; 
  private previewOutput2: camera.PreviewOutput = undefined; 
  …… 
  setImageTest(imageSet: Resource): Uint8Array { 
    let imageBuffer: Uint8Array; 
    try { 
      imageBuffer = this.context.resourceManager.getMediaContentSync(imageSet.id); // 默认屏幕密度 
    } catch (error) { 
      let code = (error as BusinessError).code; 
      let message = (error as BusinessError).message; 
      console.error(`getMediaContentSync failed, error code: ${code}, message: ${message}.`); 
    } 
    Logger.info(TAG, `imageBuffer = ${imageBuffer}`); 
    return imageBuffer; 
  }

Type 'undefined' is not assignable to type 'CameraManager'.  Variable 'imageBuffer' is used before being assigned.