[+BUGFIX] FLOW3 (Property): PropertyMapper::transformToObject() now returns the result of an object converter call if it is NULL or an object. If an error object is returned, it returns NULL and adds the error to the mapping results. Fixes #6209.
[~TASK] FLOW3 (Resource): The ResourceObjectConverter now returns NULL if no file was uploaded. In case an upload error occurred or the file extension was rejected an Error object is returned (formerly it would return FALSE or throw an exception respectively). Related to #6209.
[+FEATURE] FLOW3 (Utility): Added getUploadErrorMessage() to Files.