我在gwt项目中使用ckeditor。正在显示编辑器，但是当我尝试使用CKEditor类的getHTML()方法获取编辑的内容时，
我得到一个例外： -
Caused by: com.google.gwt.core.client.JavaScriptException: (TypeError): Cannot read property 'document' of null at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:248) at
com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136) at
com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:561) at
com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:269) at
com.google.gwt.dev.shell.JavaScriptHost.invokeNativeObject(JavaScriptHost.java:91) at com.gwtck.client.CKEditor.getNativeHTML(CKEditor.java) at com.gwtck.client.CKEditor.getHTML(CKEditor.java:162) at com.google.gwt.event.dom.client.ClickEvent.dispatch(ClickEvent.java:54) at com.google.gwt.event.dom.client.ClickEvent.dispatch(ClickEvent.java:1) at com.google.gwt.event.shared.GwtEvent.dispatch(GwtEvent.java:1) at com.google.web.bindery.event.shared.EventBus.dispatchEvent(EventBus.java:40) at com.google.web.bindery.event.shared.SimpleEventBus.doFire(SimpleEventBus.java:193) at com.google.web.bindery.event.shared.SimpleEventBus.fireEvent(SimpleEventBus.java:88) at com.google.gwt.event.shared.HandlerManager.fireEvent(HandlerManager.java:127) at com.google.gwt.user.client.ui.Widget.fireEvent(Widget.java:129) at com.google.gwt.event.dom.client.DomEvent.fireNativeEvent(DomEvent.java:116) at com.google.gwt.user.client.ui.Widget.onBrowserEvent(Widget.java:177) at com.google.gwt.user.client.DOM.dispatchEventImpl(DOM.java:1351) at com.google.gwt.user.client.DOM.dispatchEvent(DOM.java:1307) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103) at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71) at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172) at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessagesWhileWaitingForReturn(BrowserChannelServer.java:337) at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:218) at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136) at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:561) at com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:269) at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeObject(JavaScriptHost.java:91) at com.google.gwt.core.client.impl.Impl.apply(Impl.java) at com.google.gwt.core.client.impl.Impl.entry0(Impl.java:213) at sun.reflect.GeneratedMethodAccessor337.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103) at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71) at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172) at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessages(BrowserChannelServer.java:292) at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:546) at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:363) at java.lang.Thread.run(Thread.java:662)