TYPO3 Core

When adding a new related IRRE record a runtime exception is thrown after closing the related record:

(1/1) #1489751361 RuntimeException
Empty context string given

Supposing we have a relation between athletes (parent table) and competitions (child table) that is the results (MM table).
To reproduce:

1) use this TCA in a field of the parent record (athlete):

'results' => [
    'config' => [
        'type' => 'inline',
        'foreign_table' => 'tx_iantest_domain_model_result',
        'foreign_field' => 'athlete',
        'foreign_sortby' => 'sorting',
    ],
],

2) use this TCA in the field of the MM record (result):

'competition' => [
    'config' => [
        'type' => 'group',
        'internal_type' => 'db',
        'allowed' => 'tx_iantest_domain_model_competition',
        'foreign_table' => 'tx_iantest_domain_model_competition',
        'size' => 1,
        'maxitems' => 1,
        'minitems' => 0,
        'hideDeleteIcon' => true,
        'fieldControl' => [
            'elementBrowser' => [
                'disabled' => true,
            ],
            'addRecord' => [
                'disabled' => false,
                'options' => [
                    'pid' => $settings->getCompetitionsPid(),
                ],
            ],
            'editPopup' => [
                'disabled' => false,
            ],
        ],
    ]
],

3) Edit the parent record (athlete) and click the button to create a new IRRE

4) In the IRRE row click on [+] button to create a new child record (competition).

5) Now, since the parent record has been modified, TYPO3 asks the editor what to do:
[continue editing], [discard changes], [save and close]
and the only way to go to the add record form is to choose [discard changes]

6) The add record (competition) appears, edit it and save & close

7) At this point the exception is thrown.

Practically, this exception is thrown only if the parent record has been modified.