How to use SortPooling layer of Stellargraph in a Keras Model? I have my feature array, but how to give the mask attribute?

Question

I want to use SortPooling layer from Stellargraph library in a Keras-Tensorflow (2.0) model. How to give mask attribute while calling the sortpool? What does it signify?

It gives me an error asking for mask attribue

x = SortPooling(k=14, flatten_output=True)(x)