code: public boolean init(@NonNull PaymentSessionListener listener,
                          @NonNull PaymentSessionConfig paymentSessionConfig) {
          return init(listener, paymentSessionConfig, null);
      }
docs: Initialize the PaymentSession with a {@link PaymentSessionListener} to be notified of
  data changes.
  
  @param listener a {@link PaymentSessionListener} that will receive notifications of changes
  in payment session status, including networking status
  @param paymentSessionConfig a {@link PaymentSessionConfig} used to decide which items are
  necessary in the PaymentSession.
  @return {@code true} if the PaymentSession is initialized, {@code false} if a state error
  occurs. Failure can only occur if there is no initialized {@link CustomerSession}.