Importing invalid LAR file results in infinite loop

• Type: Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: 7.2.X, 7.3.X, Master
• Fix Version/s: 7.2.10 DXP FP10, 7.2.10.4 DXP SP4, 7.2.X, 7.3.10 DXP FP1, 7.3.10.1 DXP SP1, 7.3.6 CE GA7, 7.3.X, 7.4.13 DXP GA1, Master
• Component/s: Staging > Export/Import
• Labels:
  • ee-ts
  • liferay-dxp-72-sp4
  • liferay-dxp-73-sp1
  • liferay-fixpack-dxp-1-7310
  • liferay-fixpack-dxp-10-7210
• Branch Version/s:
  7.3.x, 7.2.x
• Backported to Branch:
  Committed
• Fix Priority: 3
• Git Pull Request: https://github.com/brianchandotcom/liferay-portal/pull/97081

Reproduction Steps:

Part 1: create an invalid LAR file
(or use the attached invalid_72x.lar )

1. Start up a new portal instance
2. Create a new site
3. Upload an image to document library
4. Create a new basic web content, insert the image into it
5. Export the whole site, download the LAR file
6. Rename LAR file extension to ZIP and unzip it into a directory
7. Delete all files and directories inside <LAR root folder>/group/<group ID>/com.liferay.document.library.kernel.model.DLFileEntry/
8. ZIP the folders again, and rename it to LAR

Part 2: import the invalid file

1. Start up a new portal instance
2. Create a new site
3. Import the previously created invalid LAR file

Expected result: The file is either successfully imported or the import fails with a single error
Actual result: The import never finishes, the following error message is infinitely repeated in the logs:

2020-12-17 09:52:25.550 ERROR [liferay/background_task-9][StagedModelDataHandlerUtil:610] Unable to get a staged model data handler for a null value because a model was not exported properly 

Notes:

• We don't exactly know how the invalid LAR file was created in the first place, that can be part of another investigation
• cause of the issue is this loop in DLReferencesExportImportContentProcessor