Attempt to use `apply_unitary` and return the result.

    If `val` does not support `apply_unitary` returns None.

def _apply_unitary(val: Any, args: 'ApplyChannelArgs') -> Optional[np.ndarray]:
    """Attempt to use `apply_unitary` and return the result.

    If `val` does not support `apply_unitary` returns None.
    """
    left_args = ApplyUnitaryArgs(target_tensor=args.target_tensor,
                                 available_buffer=args.auxiliary_buffer0,
                                 axes=args.left_axes)
    left_result = apply_unitary(val, left_args, None)
    if left_result is None:
        return None
    right_args = ApplyUnitaryArgs(
            target_tensor=np.conjugate(left_result),
            available_buffer=args.out_buffer,
            axes=args.right_axes)
    right_result = apply_unitary(val, right_args)
    np.conjugate(right_result, out=right_result)
    return right_result