code: @NonNull
      public Expression collate(@NonNull Collation collation) {
          if (collation == null) {
              throw new IllegalArgumentException("collation cannot be null.");
          }
          return new CollationExpression(this, collation);
      }
docs: Creates a Collate expression with the given Collation specification. Commonly
  the collate expression is used in the Order BY clause or the string comparison
  expression (e.g. equalTo or lessThan) to specify how the two strings are　compared.
  
  @param collation 　The collation object.
  @return A Collate expression.