MIGXdb not saving nested migx config tv

I have another MIGX question: I created an image+ TV and linked that to a separate migxdb config to include it in my other config “references” so I can add multiple images. Now in the CMP, the interface part works fine and I can select and crop the image, but when I try to hit save, nothing happens (I get another 500 in the dev tools).

The MODX error log shows this:

(ERROR @ .../core/components/migx/processors/mgr/default/fields.php : 46) PHP warning: Undefined array key "classname"
(ERROR @ .../core/vendor/xpdo/xpdo/src/xPDO/xPDO.php : 607) No class specified for loadClass
(ERROR @ .../core/components/migx/processors/mgr/default/update.php : 99) PHP warning: Undefined array key "classname"
(ERROR @ .../core/components/migx/processors/mgr/default/update.php : 105) PHP warning: Undefined variable $packageName
(ERROR @ .../core/vendor/xpdo/xpdo/src/xPDO/xPDO.php : 607) No class specified for loadClass

This makes me think MIGX wants me to define a package and a classname in the settings of the newly created image config, but I am just using this config to create the nested TV, so I’m not sure what to do here? I thought in this case I wouldn’t need a custom package to be defined?

In case that’s needed, here is also the server error log:

show server log
POST /assets/components/migx/connector.php HTTP/1.0 - 500

PHP Fatal error: Uncaught Error: Call to a member function get() on null in .../core/components/migx/processors/mgr/default/update.php:289, referer: .../manager/?a=index&namespace=migx&configs=referenzen||kategorien
Stack trace:, referer: .../manager/?a=index&namespace=migx&configs=referenzen||kategorien
#0 .../core/components/migx/processors/mgr/migxdb/update.class.php(25): include_once(), referer: .../manager/?a=index&namespace=migx&configs=referenzen||kategorien
#1 .../core/src/Revolution/Processors/Processor.php(189): migxUpdateProcessor->process(), referer: .../manager/?a=index&namespace=migx&configs=referenzen||kategorien
#2 .../core/src/Revolution/modX.php(1816): MODX\\Revolution\\Processors\\Processor->run(), referer: .../manager/?a=index&namespace=migx&configs=referenzen||kategorien
#3 .../core/src/Revolution/modConnectorResponse.php(151): MODX\\Revolution\\modX->runProcessor('mgr/migxdb/upda...', Array, Array), referer: .../manager/?a=index&namespace=migx&configs=referenzen||kategorien
#4 .../core/src/Revolution/modConnectorRequest.php(89): MODX\\Revolution\\modConnectorResponse->outputContent(Array), referer: .../manager/?a=index&namespace=migx&configs=referenzen||kategorien
#5 .../core/src/Revolution/modConnectorRequest.php(77): MODX\\Revolution\\modConnectorRequest->prepareResponse(Array), referer: .../manager/?a=index&namespace=migx&configs=referenzen||kategorien
#6 .../assets/components/migx/connector.php(57): MODX\\Revolution\\modConnectorRequest->handleRequest(Array), referer: .../manager/?a=index&namespace=migx&configs=referenzen||kategorien
#7 {main}, referer: .../manager/?a=index&namespace=migx&configs=referenzen||kategorien
thrown in .../core/components/migx/processors/mgr/default/update.php on line 289, referer: .../manager/?a=index&namespace=migx&configs=referenzen||kategorien

MODX 3.0.5-pl
MIGX 3.0.2-beta1

For your nested MIGX config, do you use migxdb (for the “Input TV type”) to save the images to a custom database table, or do you use migx to save the images as JSON to a column of the “reference”-class?

I used migxdb, but obviously I should use migx. Thank you!