private Object getTag() {
        if (tagId == null) {
            return view.getTag();
        } else {
            return view.getTag(tagId);
        }
    }
Returns any stored request using {@link View#getTag()}.

<p>
    For Glide to function correctly, Glide must be the only thing that calls {@link View#setTag(Object)}. If the
    tag is cleared or set to another object type, Glide will not be able to retrieve and cancel previous loads
    which will not only prevent Glide from reusing resource, but will also result in incorrect images being
    loaded and lots of flashing of images in lists. As a result, this will throw an
    {@link IllegalArgumentException} if {@link View#getTag()}} returns a non null object
    that is not an {@link Request}.
</p>
core/src/main/java/com/bumptech/glide/request/target/ViewTarget.java