Nested eager load throws error when nested tier is missing

[evanwarner]

Description

I'm executing a nested eager load: querying for a list of entries, eager loading the user from a specific field, and also that user's profile photo.

{% set recentPosts = craft.entries({
  section: 'blogPosts',
  with: ['guestAuthor.photo'],
  limit: 5,
}) %}

If any of the users don't have a profile photo, I get the following error:
TypeError Argument 1 passed to craft\helpers\StringHelper::toLowerCase() must be of the type string, null given, called in [...]/vendor/craftcms/cms/src/helpers/Db.php on line 448

I'd expect to be able to just handle a missing photo in my template code after the query executes.

Steps to reproduce

1. Create an entry
2. Add a Users field to the entry and select a user that does not have a photo
3. Query for that entry, and eager load the user and their photo

Additional info

• Craft version: 3.0.1
• PHP version: 7.1.12
• Database driver & version: MySQL 5.6.38
• Plugins & versions: CodeMirror 1.0.0, Element API 2.5.2, GatherContent 1.0.5, Redactor 1.1.0

Stack Trace

TypeError: Argument 1 passed to craft\helpers\StringHelper::toLowerCase() must be of the type string, null given, called in [...]/vendor/craftcms/cms/src/helpers/Db.php on line 448 and defined in [...]/vendor/craftcms/cms/src/helpers/StringHelper.php:742
Stack trace:
#0 [...]/vendor/craftcms/cms/src/helpers/Db.php(448): craft\helpers\StringHelper::toLowerCase(NULL)
#1 [...]/vendor/craftcms/cms/src/elements/db/ElementQuery.php(912): craft\helpers\Db::parseParam('elements.id', Array)
#2 [...]/vendor/yiisoft/yii2/db/QueryBuilder.php(227): craft\elements\db\ElementQuery->prepare(Object(craft\db\mysql\QueryBuilder))
#3 [...]/vendor/yiisoft/yii2/db/Query.php(146): yii\db\QueryBuilder->build(Object(craft\elements\db\AssetQuery))
#4 [...]/vendor/yiisoft/yii2/db/Query.php(237): yii\db\Query->createCommand(Object(craft\db\Connection))
#5 [...]/vendor/craftcms/cms/src/db/Query.php(155): yii\db\Query->all(NULL)
#6 [...]/vendor/craftcms/cms/src/elements/db/ElementQuery.php(1011): craft\db\Query->all(NULL)
#7 [...]/vendor/craftcms/cms/src/services/Elements.php(1232): craft\elements\db\ElementQuery->all()
#8 [...]/vendor/craftcms/cms/src/elements/db/ElementQuery.php(1969): craft\services\Elements->eagerLoadElements('craft\\elements\\...', Array, Array)
#9 [...]/vendor/craftcms/cms/src/elements/db/ElementQuery.php(985): craft\elements\db\ElementQuery->_createElements(Array)
#10 [...]/vendor/yiisoft/yii2/db/Query.php(238): craft\elements\db\ElementQuery->populate(Array)
#11 [...]/vendor/craftcms/cms/src/db/Query.php(155): yii\db\Query->all(NULL)
#12 [...]/vendor/craftcms/cms/src/elements/db/ElementQuery.php(1011): craft\db\Query->all(NULL)
#13 [...]/vendor/twig/twig/lib/Twig/Extension/Core.php(1605): craft\elements\db\ElementQuery->all()
#14 [...]/vendor/craftcms/cms/src/helpers/Template.php(73): twig_get_attribute(Object(craft\web\twig\Environment), Object(Twig_Source), Object(craft\elements\db\EntryQuery), 'all', Array, 'method', false, false)
#15 [...]/storage/runtime/compiled_templates/a0/a0c29669680e97ad9713d130dae9ed8ca4989d1a509f9c7dcbc2deca0d524e23.php(137): craft\helpers\Template::attribute(Object(craft\web\twig\Environment), Object(Twig_Source), Object(craft\elements\db\EntryQuery), 'all', Array, 'method')
#16 [...]/vendor/twig/twig/lib/Twig/Template.php(189): __TwigTemplate_678037ad78e0639e31fd7c649f320cdefaaaf12c29f3fb3fe2d69985fb630674->block_content(Array, Array)
#17 [...]/storage/runtime/compiled_templates/30/3061c03a1f5b2a1308a1fb6febe98702174428db178d73977d812ac0cd97d35c.php(113): Twig_Template->displayBlock('content', Array, Array)
#18 [...]/vendor/twig/twig/lib/Twig/Template.php(390): __TwigTemplate_9965976e6d9afcb496b44c889613bedb125f2eb34ed35ba3bf59d0827eb212f4->doDisplay(Array, Array)
#19 [...]/vendor/craftcms/cms/src/web/twig/Template.php(49): Twig_Template->displayWithErrorHandling(Array, Array)
#20 [...]/vendor/twig/twig/lib/Twig/Template.php(367): craft\web\twig\Template->displayWithErrorHandling(Array, Array)
#21 [...]/vendor/craftcms/cms/src/web/twig/Template.php(31): Twig_Template->display(Array, Array)
#22 [...]/storage/runtime/compiled_templates/a0/a0c29669680e97ad9713d130dae9ed8ca4989d1a509f9c7dcbc2deca0d524e23.php(32): craft\web\twig\Template->display(Array, Array)
#23 [...]/vendor/twig/twig/lib/Twig/Template.php(390): __TwigTemplate_678037ad78e0639e31fd7c649f320cdefaaaf12c29f3fb3fe2d69985fb630674->doDisplay(Array, Array)
#24 [...]/vendor/craftcms/cms/src/web/twig/Template.php(49): Twig_Template->displayWithErrorHandling(Array, Array)
#25 [...]/vendor/twig/twig/lib/Twig/Template.php(367): craft\web\twig\Template->displayWithErrorHandling(Array, Array)
#26 [...]/vendor/craftcms/cms/src/web/twig/Template.php(31): Twig_Template->display(Array, Array)
#27 [...]/vendor/twig/twig/lib/Twig/Template.php(375): craft\web\twig\Template->display(Array)
#28 [...]/vendor/twig/twig/lib/Twig/Environment.php(289): Twig_Template->render(Array)
#29 [...]/vendor/craftcms/cms/src/web/View.php(305): Twig_Environment->render('blog/_index', Array)
#30 [...]/vendor/craftcms/cms/src/web/View.php(352): craft\web\View->renderTemplate('blog/_index', Array)
#31 [...]/vendor/craftcms/cms/src/web/Controller.php(113): craft\web\View->renderPageTemplate('blog/_index', Array)
#32 [...]/vendor/craftcms/cms/src/controllers/TemplatesController.php(78): craft\web\Controller->renderTemplate('blog/_index', Array)
#33 [internal function]: craft\controllers\TemplatesController->actionRender('blog/_index', Array)
#34 [...]/vendor/yiisoft/yii2/base/InlineAction.php(57): call_user_func_array(Array, Array)
#35 [...]/vendor/yiisoft/yii2/base/Controller.php(157): yii\base\InlineAction->runWithParams(Array)
#36 [...]/vendor/craftcms/cms/src/web/Controller.php(74): yii\base\Controller->runAction('render', Array)
#37 [...]/vendor/yiisoft/yii2/base/Module.php(528): craft\web\Controller->runAction('render', Array)
#38 [...]/vendor/craftcms/cms/src/web/Application.php(238): yii\base\Module->runAction('templates/rende...', Array)
#39 [...]/vendor/yiisoft/yii2/web/Application.php(103): craft\web\Application->runAction('templates/rende...', Array)
#40 [...]/vendor/craftcms/cms/src/web/Application.php(227): yii\web\Application->handleRequest(Object(craft\web\Request))
#41 [...]/vendor/yiisoft/yii2/base/Application.php(386): craft\web\Application->handleRequest(Object(craft\web\Request))
#42 [...]/web/index.php(21): yii\base\Application->run()
#43 {main}

[evanwarner]

I should note that the query is fine if any of the posts are missing an assigned user, so long as all of the users that are assigned have photos.

[evanwarner]

With a little more experimentation, it seems like user photos might be a special field, not treated like a normal Asset field. So perhaps my assumption that I could eager load the image asset is incorrect.

[brandonkelly]

Yep users do support eager-loading their photos. That error should be fixed for the next release. Thanks for reporting!