joinFields with myfield='' causes "Unknown column" error

[tuomassalo]

ProcessWire forms an invalid SELECT clause if a field is in joinFields AND is also in a condition that demands it to be empty.

Both of these:

$pages->find("template=basic-page, title='', field=title");

$pages->find("template=basic-page,title=''", ["joinFields" => ["title"]]);

result in:

PDOException: SQLSTATE[42S22]: Column not found: 1054 Unknown column 'field_title.data' in 'field list';

The invalid select clause looks like this: (slightly formatted for clarity)

SELECT
    (
        SELECT COUNT(*) FROM pages AS children
        WHERE children.parent_id = pages.id
    ) AS numChildren,
    field_title.data AS title__data,
    pages.*,
    UNIX_TIMESTAMP (pages.created) AS created,
    UNIX_TIMESTAMP (pages.modified) AS modified,
    UNIX_TIMESTAMP (pages.published) AS published,
    pages_sortfields.sortfield AS sortfield
FROM
    pages
    LEFT JOIN pages_sortfields ON pages_sortfields.pages_id = pages.id
    LEFT JOIN field_title AS field_title__blank1 ON field_title__blank1.pages_id = pages.id
WHERE
    (pages.templates_id = 29)
    AND (pages.status < 1024)
    AND (
        field_title__blank1.data IS NULL
        OR (field_title__blank1.data = '')
    )
GROUP BY
    pages.id

What I expected?

I expected the find call to succeed and the joined field be available without further queries.

Notes

In the example above, title was used. But it seems any field will result in the same error.

[ryancramerdesign]

@tuomassalo Thanks, I've pushed a fix for this issue.