Similar to get_annotated_chain_sequence_string except that we only return the Sequence and do not state which sequence it was.

def get_chain_sequence_string(self, chain_id, use_seqres_sequences_if_possible, raise_Exception_if_not_found = True):
        '''Similar to get_annotated_chain_sequence_string except that we only return the Sequence and do not state which sequence it was.'''
        chain_pair = self.get_annotated_chain_sequence_string(chain_id, use_seqres_sequences_if_possible, raise_Exception_if_not_found = raise_Exception_if_not_found)
        if chain_pair:
            return chain_pair[1]
        return None