White screen when accessing JSON-LD representation of node in some circumstances

[alxp]

PR: Islandora/islandora#862

Steps to Reproduce

In an Islandora site, clone the https://github.com/roblib/islandora_premis module into the modules/contrib folder and check out the 'unpublished' branch. and then enable the module.

Create a new Repository Item object, and uncheck 'Published' before saving.

Append '/premis' to the end of the new object's url, e.g. /node/3/premis.

Expected behaviour

The PREMIS data about the object, represented as Turtle text should be displayed.

Actual output

The message "The website encountered an error" is shown.

Findings

I'm working with a module that sets up a controller endpoint that includes a nid.

As per proper Drupal 8.x+ practise, it has had entity access check in the routing.yml file, e.g.

islandora_premis.premis:
  path: '/node/{node}/premis'
  defaults:
    _controller: '\Drupal\islandora_premis\Controller\IslandoraPremisPremisController::main'
  options:
    parameters:
      node:
        type: 'entity:node'

In islandora.module there is an alter reaction hook that runs context reactions on the JSON-LD normalized array.

Currently it will set a cache tag on the array. However, when entity access check is added, no 'cacheability' array key is set, and the module white screens.

[jordandukart]

Merged in Islandora/islandora#862.