[TYPO3-Solr] Problem with SOLR_RELATION

[Tim Werdin]

This is a splitup from a previous ticket of mine.

I have a field images in my database. This field holds a commaseperated 
list of tx_dam uids with images.
images = 4,5,6,7 e.g.

I tried the following:

plugin.tx_solr.index.queue.wv_stx3.fields {
  image_stringM = SOLR_RELATION
  image_stringM {
    localField = images
    multiValue = 1
    foreignLabelField = file_name
  }
}

Which gives me the error message: PHP Catchable Fatal Error: Argument 1 
passed to 
tx_solr_contentobject_Relation::resolveForeignTableLabelField() must be 
an array, null given, called in […]