TYPO3 Core

Trying to use a slash in routeFieldPattern and routeFieldResult results in a fatal error.
There seems to be no valid regex pattern possible to achieve a routeFieldResult containing a slash.

The goal is to not have the category path in the URL when the category parameter is not provided.
Expecting URLs like:
Both parameter set: /producer/producer-naame/category/category-name
Only producer parameter set: /producer/producer-naame
Only category parameter set: /category/category-name

SomePlugin:
    type: Plugin
    limitToPages: [95]
    routePath: "/{producer}{category}" 
    namespace: "tx_myext_pi1" 
    requirements:
      producer: "[0-9]" 
      category: "[0-9]" 
    aspects:
      producer:
        type: PersistedPatternMapper
        tableName: "tx_myext_producers" 
        routeFieldPattern: "producer/^(?P<slug>.+)$" 
        routeFieldResult: "producer/{slug}" 
      category:
        type: PersistedPatternMapper
        tableName: "tx_myext_cats" 
        routeFieldPattern: "category/^(?P<slug>.+)$" 
        routeFieldResult: "category/{slug}" 

Not sure if this is a bug or a missing feature.