Fix "(TypeError) : opEnum is null" error when editing a Full text widget

(TypeError) : opEnum is null

Uncaught exception: com.google.gwt.core.client.JavaScriptException: (TypeError) : opEnum is null
    at Unknown.shouldAskUserIfMulti(studio-0.js)
    at Unknown.addExtraFieldsForDocumentOrGeneric_0(studio-0.js)
    at Unknown.createContent_30(studio-0.js)
    at Unknown.createContentArea(studio-0.js)
    at Unknown.createDialogPanel(studio-0.js)
    at Unknown.show_3(studio-0.js)
    at Unknown.center_0(studio-0.js)
    at Unknown.openWidgetEditor_2(studio-0.js)
    at Unknown.onClick_128(studio-0.js)
    at Unknown.dispatch_4(studio-0.js)
    at Unknown.dispatch_5(studio-0.js)
    at Unknown.dispatch(studio-0.js)
    at Unknown.dispatchEvent_3(studio-0.js)
    at Unknown.doFire(studio-0.js)
    at Unknown.fireEvent_2(studio-0.js)
    at Unknown.fireEvent_1(studio-0.js)
    at Unknown.fireEvent_0(studio-0.js)
    at Unknown.fireNativeEvent(studio-0.js)
    at Unknown.onBrowserEvent(studio-0.js)
    at Unknown.onBrowserEvent_1(studio-0.js)
    at Unknown.dispatchEventImpl(studio-0.js)
    at Unknown.dispatchEvent_5(studio-0.js)
    at Unknown.dispatchEvent_7(studio-0.js)
    at Unknown.apply_0(studio-0.js)
    at Unknown.entry0(studio-0.js)
    at Unknown.entry_0/<(studio-0.js)
    at Unknown.anonymous(Unknown)