setValue() function fails, preventing to set selection on the tree

"(TypeError): this.com_google_gwt_user_client_ui_UIObject_element is null\n fileName: http://localhost:8080/xwiki/resources/js/xwiki/wysiwyg/gwt/com.xpn.xwiki.wysiwyg.Wysiwyg/BADB6FEB537D22ABC5DD832762F80972.cache.html\n lineNumber: 4755\n stack: com_google_gwt_user_client_ui_FocusWidget_setTabIndex__I(0)@http://localhost:8080/xwiki/resources/js/xwiki/wysiwyg/gwt/com.xpn.xwiki.wysiwyg.Wysiwyg/BADB6FEB537D22ABC5DD832762F80972.cache.html:4755\ncom_google_gwt_user_client_ui_TextBox_$TextBox__Lcom_google_gwt_user_client_ui_TextBox_2Lcom_google_gwt_dom_client_Element_2([object Object],null)@http://localhost:8080/xwiki/resources/js/xwiki/wysiwyg/gwt/com.xpn.xwiki.wysiwyg.Wysiwyg/BADB6FEB537D22ABC5DD832762F80972.cache.html:10050\ncom_xpn_xwiki_wysiwyg_client_widget_explorer_XWikiExplorer_$setValue__Lcom_xpn_xwiki_wysiwyg_client_widget_explorer_XWikiExplorer_2Ljava_lang_String_2([object Object],"Blog.RssCode")@http://localhost:8080/xwiki/resources/js/xwiki/wysiwyg/gwt/com.xpn.xwiki.wysiwyg.Wysiwyg/BADB6FEB537D22ABC5DD832762F80972.cache.html:29928\ncom_xpn_xwiki_wysiwyg_client_plugin_link_ui_SelectorWizardStep_init__Ljava_lang_Object_2Lcom_google_gwt_user_client_rpc_AsyncCallback_2([object Object],[object Object])@http://localhost:8080/xwiki/resources/js/xwiki/wysiwyg/gwt/com.xpn.xwiki.wysiwyg.Wysiwyg/BADB6FEB537D22ABC5DD832762F80972.cache.html:24145\ncom_xpn_xwiki_wysiwyg_client_widget_wizard_Wizard_$initAndDisplayCurrentStep__Lcom_xpn_xwiki_wysiwyg_client_widget_wizard_Wizard_2Ljava_lang_Object_2([object Object],[object Object])@http://localhost:8080/xwiki/resources/js/xwiki/wysiwyg/gwt/com.xpn.xwiki.wysiwyg.Wysiwyg/BADB6FEB537D22ABC5DD832762F80972.cache.html:23940\ncom_xpn_xwiki_wysiwyg_client_widget_wizard_Wizard_$start__Lcom_xpn_xwiki_wysiwyg_client_widget_wizard_Wizard_2Ljava_lang_String_2Ljava_lang_Object_2([object Object],"wikipage",[object Object])@http://localhost:8080/xwiki/resources/js/xwiki/wysiwyg/gwt/com.xpn.xwiki.wysiwyg.Wysiwyg/BADB6FEB537D22ABC5DD832762F80972.cache.html:24008\ncom_xpn_xwiki_wysiwyg_client_plugin_link_LinkPlugin_$dispatchLinkWizard__Lcom_xpn_xwiki_wysiwyg_client_plugin_link_LinkPlugin_2Lcom_xpn_xwiki_wysiwyg_client_plugin_link_LinkConfig_2([object Object],[object Object])@http://localhost:8080/xwiki/resources/js/xwiki/wysiwyg/gwt/com.xpn.xwiki.wysiwyg.Wysiwyg/BADB6FEB537D22ABC5DD832762F80972.cache.html:23249\ncom_xpn_xwiki_wysiwyg_client_plugin_link_LinkPlugin_$onLinkEdit__Lcom_xpn_xwiki_wysiwyg_client_plugin_link_LinkPlugin_2([object Object])@http://localhost:8080/xwiki/resources/js/xwiki/wysiwyg/gwt/com.xpn.xwiki.wysiwyg.Wysiwyg/BADB6FEB537D22ABC5DD832762F80972.cache.html:23340\ncom_xpn_xwiki_wysiwyg_client_plugin_link_LinkMenuExtension$4_execute__()@http://localhost:8080/xwiki/resources/js/xwiki/wysiwyg/gwt/com.xpn.xwiki.wysiwyg.Wysiwyg/BADB6FEB537D22ABC5DD832762F80972.cache.html:23153\ncom_google_gwt_user_client_CommandExecutor_$doExecuteCommands__Lcom_google_gwt_user_client_CommandExecutor_2D([object Object],1238762027962)@http://localhost:8080/xwiki/resources/js/xwiki/wysiwyg/gwt/com.xpn.xwiki.wysiwyg.Wysiwyg/BADB6FEB537D22ABC5DD832762F80972.cache.html:1926\ncom_google_gwt_user_client_CommandExecutor$2_run__()@http://localhost:8080/xwiki/resources/js/xwiki/wysiwyg/gwt/com.xpn.xwiki.wysiwyg.Wysiwyg/BADB6FEB537D22ABC5DD832762F80972.cache.html:2032\ncom_google_gwt_user_client_Timer_$fireImpl__Lcom_google_gwt_user_client_Timer_2([object Object])@http://localhost:8080/xwiki/resources/js/xwiki/wysiwyg/gwt/com.xpn.xwiki.wysiwyg.Wysiwyg/BADB6FEB537D22ABC5DD832762F80972.cache.html:160\ncom_google_gwt_user_client_Timer_fire__()@http://localhost:8080/xwiki/resources/js/xwiki/wysiwyg/gwt/com.xpn.xwiki.wysiwyg.Wysiwyg/BADB6FEB537D22ABC5DD832762F80972.cache.html:198\n(5)@http://localhost:8080/xwiki/resources/js/xwiki/wysiwyg/gwt/com.xpn.xwiki.wysiwyg.Wysiwyg/BADB6FEB537D22ABC5DD832762F80972.cache.html:192\n"