def forward(self, inputs, token_types, valid_length=None):  # pylint: disable=arguments-differ
        """Generate the unnormalized score for the given the input sequences.

        Parameters
        ----------
        inputs : NDArray, shape (batch_size, seq_length)
            Input words for the sequences.
        token_types : NDArray, shape (batch_size, seq_length)
            Token types for the sequences, used to indicate whether the word belongs to the
            first sentence or the second one.
        valid_length : NDArray or None, shape (batch_size,)
            Valid length of the sequence. This is used to mask the padded tokens.

        Returns
        -------
        outputs : NDArray
            Shape (batch_size, seq_length, 2)
        """
        bert_output = self.bert(inputs, token_types, valid_length)
        output = self.span_classifier(bert_output)
        return output