我想将Ionic与WordPress API Angular连接起来。但是我得到了这个错误：
TypeError：无法读取未定义的属性“length”
at WpProvider.webpackJsonp.211.WpProvider.getUserImage (http://localhost:8100/build/main.js:293:51)
at BlogPage.webpackJsonp.150.BlogPage.getUserImage (http://localhost:8100/build/main.js:36:32)
at Object.eval [as updateRenderer] (ng:///AppModule/BlogPage.ngfactory.js:47:25)
at Object.debugUpdateRenderer [as updateRenderer] (http://localhost:8100/build/vendor.js:15041:21)
at checkAndUpdateView (http://localhost:8100/build/vendor.js:14177:14)
at callViewAction (http://localhost:8100/build/vendor.js:14522:21)
at execEmbeddedViewsAction (http://localhost:8100/build/vendor.js:14480:17)
at checkAndUpdateView (http://localhost:8100/build/vendor.js:14173:5)
at callViewAction (http://localhost:8100/build/vendor.js:14522:21)
at execComponentViewsAction (http://localhost:8100/build/vendor.js:14454:13)
为什么会出现这个问题？