src/transformers/models/mobilebert/modeling_tf_mobilebert.py/TFMobileBertPooler/call
class TFMobileBertPooler:    def call(self, hidden_states):
        # We "pool" the model by simply taking the hidden state corresponding
        # to the first token.
        first_token_tensor = hidden_states[:, 0]
        if not self.do_activate:
            return first_token_tensor
        else:
            pooled_output = self.dense(first_token_tensor)
            return pooled_output