message: Replace join.rs Option->into_iter() to iter::once
diff: use boolinator::Boolinator;
  use nom_sql::{Column, JoinClause, JoinConstraint, JoinOperator, Table};
  use std::fmt::Debug;
  +use std::iter::once;
  use std::rc::Rc;
  use thiserror::Error as ThisError;
  @@ -51,7 +52,7 @@ macro_rules! try_some {
  impl<'a, T: 'static + Debug> Join<'a, T> {
  fn err(e: Error) -> JoinResult<'a, T> {
  - Box::new(Some(Err(e)).into_iter())
  + Box::new(once(Err(e)))
  }
  pub fn new(
  @@ -70,7 +71,7 @@ impl<'a, T: 'static + Debug> Join<'a, T> {
  pub fn apply(&self, init_context: Result<BlendContext<'a, T>>) -> JoinResult<'a, T> {
  let init_context = init_context.map(|c| Rc::new(c));
  - let init_rows = Box::new(Some(init_context).into_iter());
  + let init_rows = Box::new(once(init_context));
  self.join_clauses.iter().zip(self.join_columns.iter()).fold(
  init_rows,
  @@ -152,7 +153,7 @@ fn join<'a, T: 'static + Debug>(
  let is_last = true;
  let item = (is_last, init_context);
  - Some(Ok(item)).into_iter()
  + once(Ok(item))
  })
  .enumerate()
  .filter_map(|(i, item)| {
  