Attempting to create a ContentType with more than one Field Definition fails under certain conditions, one of which is described below:

• Create a custom ContentType Group (e.g. "Tutorials")
• Within that ContentType Group, create a ContentType (e.g. "Tutorial")
• Check the "Container" option on the ContentType, and add a Field Definition (e.g. Text line: "Title", required)
• Attempt to add a second Field Definition (e.g. Selection: "Skill Level", 3 options: "Beginner", "Intermediate", "Advanced", required)
• Try to "OK" or "Apply"

Result: Red error bar at bottom of Admin UI: "Failed to load 'http://example.site.tld/pjax/contenttype/update/##/eng-GB'" where ## is the id of the ContentType. Developer tools show on the console: "Failed to load resource: the server responded with a status of 500 (Internal Server Error)"

Form Data:

ezrepoforms_contenttype_update[saveContentType]:
ezrepoforms_contenttype_update[name]:Tutorial
ezrepoforms_contenttype_update[identifier]:tutorial
ezrepoforms_contenttype_update[description]:A Tutorial
ezrepoforms_contenttype_update[nameSchema]:<title>
ezrepoforms_contenttype_update[urlAliasSchema]:
ezrepoforms_contenttype_update[defaultSortField]:2
ezrepoforms_contenttype_update[defaultSortOrder]:0
ezrepoforms_contenttype_update[defaultAlwaysAvailable]:1
ezrepoforms_contenttype_update[fieldDefinitionsData][0][position]:1
ezrepoforms_contenttype_update[fieldDefinitionsData][0][name]:Title
ezrepoforms_contenttype_update[fieldDefinitionsData][0][identifier]:title
ezrepoforms_contenttype_update[fieldDefinitionsData][0][description]:The title of the tutorial
ezrepoforms_contenttype_update[fieldDefinitionsData][0][isRequired]:1
ezrepoforms_contenttype_update[fieldDefinitionsData][0][isSearchable]:1
ezrepoforms_contenttype_update[fieldDefinitionsData][0][isTranslatable]:1
ezrepoforms_contenttype_update[fieldDefinitionsData][0][fieldGroup]:content
ezrepoforms_contenttype_update[fieldDefinitionsData][0][minLength]:1
ezrepoforms_contenttype_update[fieldDefinitionsData][0][maxLength]:
ezrepoforms_contenttype_update[fieldDefinitionsData][0][defaultValue]:
ezrepoforms_contenttype_update[fieldTypeSelection]:ezauthor

Log entry from prod:

request.CRITICAL: Uncaught PHP Exception
eZ\Publish\API\Repository\Exceptions\PropertyNotFoundException:
"Property 'field' not found on class 'EzSystems\RepositoryForms\Data\FieldDefinitionData'"
at /var/www/ezplatform/vendor/ezsystems/ezpublish-kernel/eZ/Publish/API/Repository/Values/ValueObject.php
line 101

{"exception":"[object] (eZ\\Publish\\API\\Repository\\Exceptions\\PropertyNotFoundException(code: 0): Property 'field' not found on class 'EzSystems\\RepositoryForms\\Data\\FieldDefinitionData' at var/www/ezplatform/vendor/ezsystems/ezpublish-kernel/eZ/Publish/API/Repository/Values/ValueObject.php:101)"}

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Seen also in Community Slack as well: https://ezcommunity.slack.com/archives/C06BF1CLB/p1505994530000263