def _get_pooler(self, units, prefix):
with self.name_scope():<EOL><INDENT>pooler = nn.Dense(units=units, flatten=False, activation='<STR_LIT>',<EOL>prefix=prefix)<EOL><DEDENT>return pooler<EOL>
Construct pooler.

        The pooler slices and projects the hidden output of first token
        in the sequence for segment level classification.