Convert String to Date with ruby

I am trying to parse string to date with ruby. With the code

event.set("[parsed][Journey][#{x}][Abfahrtsdatum]",Date.parse(event.get("[parsed][Journey][#{x}][Abfahrtsdatum]")));

I get the following error:

Ruby exception occurred: Missing Converter handling for full class name=org.jruby.ext.date.RubyDate, simple name=RubyDate

The value of field [parsed][Journey][#{x}][Abfahrtsdatum] looks like this: "18.11.19"