How to avoid "warning: [cast] redundant cast to String" for data binding

Question

Android Studio generates lots of warning like the following:

fooBindingImpl.java:106: warning: [cast] redundant cast to String fooActivityOfUserName.set(((java.lang.String) (callbackArg_0)));

FooActivity.java has the following:

public final ObservableField<String> ofUserName = new ObservableField<>("");

I also tried the following:

public final ObservableField<String> ofUserName = new ObservableField<String>("");

Its layout has the following:

<EditText
    android:id="@+id/etUserName"
    style="@style/EditText"
    android:hint="@string/user_name"
    android:inputType="textPersonName"
    android:nextFocusDown="@+id/editTextPassword"
    android:text="@={newActivity.ofUserName}" />

Is there a way to avoid the warning?