Cannot read properties of undefined (reading 'urlType')

1.0.0-alpha.8 fails for us with this stacktrace. items seems to be not undefined, but an empty array. 1.0.0-alpha.7 worked fine.

[08:07:39.796] FATAL (antora): Cannot read properties of undefined (reading 'urlType')
    Cause: TypeError
        at aggregateAsciiDoc (/home/user/workspace/common/rp-docs-master/node_modules/@antora/assembler/lib/produce-aggregate-document.js:501:54)
        at produceAggregateDocument (/home/user/workspace/common/rp-docs-master/node_modules/@antora/assembler/lib/produce-aggregate-document.js:32:16)
        at /home/user/workspace/common/rp-docs-master/node_modules/@antora/assembler/lib/produce-aggregate-documents.js:54:11
        at Array.map (<anonymous>)
        at /home/user/workspace/common/rp-docs-master/node_modules/@antora/assembler/lib/produce-aggregate-documents.js:53:59
        at Array.reduce (<anonymous>)
        at produceAggregateDocuments (/home/user/workspace/common/rp-docs-master/node_modules/@antora/assembler/lib/produce-aggregate-documents.js:17:101)
        at GeneratorContext.assembleContent (/home/user/workspace/common/rp-docs-master/node_modules/@antora/assembler/lib/assemble-content.js:19:30)
        at async GeneratorContext.notify (/home/user/workspace/common/rp-docs-master/node_modules/@antora/site-generator/lib/generator-context.js:59:39)
        at async generateSite (/home/user/workspace/common/rp-docs-master/node_modules/@antora/site-generator/lib/generate-site.js:52:5)